Loop End Clock Mainspring

Loop End Clock Mainspring



Loop End Clock Mainspring

First, measure the width. Then match it up with the proper section of the chart. After matching the width, see what is the closest spring in that section in thickness and length.

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Loop End Clock Mainspring - Use on Antique spring driven clocks. These have a loop on the end to wrap around the movements plate arbor. - Clockworks
Loop-End MainspringDescriptionDamage AssessmentMeasuring the Mainspring

Please view these information tabs to help get Clock Loop-End Mainspring Replacements

Loop-End Clock Mainspring Description

The Loop-End clock mainspring description consists of a long flat spring with a loop on one end. This loop wraps around the outer plate pillar of the movement. In other words, this is the type of mainspring that can be seen.

Thus, it is not inside a barrel. Likewise, if the spring is in a barrel, the mainspring can't be seen. Hence, a mainspring that cannot be seen is a hole end mainspring. So, hole end mainsprings can be found on the hole end mainspring page.

Specifically follow the directions to match up your spring to a new one. Should you need assistance please feel free to email us questions. Of course, our experienced clockmakers are happy to help.

How to know if it is broken

Use the clock key to wind the mainspring. Naturally, the spring is broken when it winds for a bit and then snaps back.

Certainly, it could be wound forever and it will not stay in a coil. This is how a spring reacts when it breaks. When the spring breaks, it can protrude a great deal outside of the movement.

On the other hand, if it is a hole end mainspring it will usually stay within the barrel. In extreme cases, the mainspring will damage the clock case. Of course, this is not a common occurrence, but it can happen. Consequently, we do not repair cases.

In fact, that would need a woodworker to fix. Above all, mainsprings can be very dangerous when they snap. Also, it is possible for mainsprings to cause damage to the gears in the movement. Naturally, if this happens then a restoration needs to happen. Please email us for more information on this topic.

How Loop-End Clock Mainsprings come

These mainsprings come wound up with a tie wire around it. Once the movement is put back together, make sure it is wound up all the way and cut the tie wire. As mentioned previously, treat mainsprings with respect and caution.

Always wear safety glasses and gloves. Seriously, mainsprings are nothing to fool with. They can punch, whack, cut, and snap at you. All things said, mainsprings are quite possibly the only dangerous part to work on in a clock.

Repair service

clockworks.com offers a clock repair service. For a loop-end clock mainspring, it would be a movement restoration instead of a mainspring swap.

This might be the best solution. Since mainsprings can cause a great deal of damage when they break. There could be much more damage than just a broken mainspring. A restoration will take care of any damage that may occur from the break.

If you choose to go this route please email a picture of the movement. Of course, we will get back to you on the best solution. A picture is always a good start so we know exactly what you have. Once we see the movement, we can provide a quote to restore it.

If the mainsprings are breaking then it is quite possible that the movement is in need of other work. This is typical of anything mechanical. Once one thing breaks, usually other parts are not far behind.

Clockworks will advise what is the best and least expensive way to get the clock back up and running. Clockworks always has your best interest at heart. Occasionally movements are beyond repair. This does not happen often, however.

The content of this website is copyright by Clockworks and written by James Stoudenmire in year 2022

Clock Mainspring Break - Damage Assessment

When a mainspring breaks within a clock movement, it could cause damage. This damage could be within the movement itself or to the clock case. However, it is uncommon, but sometimes even the sides of the wood case can sustain damage when a mainspring breaks.

The German movement

As for the movement itself, we need to check the gear teeth and the gear arbors. Any damage will be on the lower part of the gear train if anywhere. Initially, the teeth of the gear that the mainspring is on, is a good place to start.

The next gear up is also a frequent damage area. As you go up the gear train, to the smaller wheels, damage is unlikely. So the force of the breaking impact happens in the lower wheels, typically the main wheel and the next one up.

Antiques with lantern pinions

Lantern pinions are the type of gear that is made of vertical wires instead of teeth. So it would be the smaller side of the two intersecting gears and would be going up the train not down. Thus the vertical wires within the circular brass bushings act as teeth instead of having a gear.

Subsequently, the advantage is the wire will spin within the bushings and decreasing friction and wear. However, not all clocks have lantern pinions, this would apply to some antique American time strike units only.

Lantern pinion damage check

If the clock has lantern pinions it is possible that some pins have bent or broken off completely. It would happen on the next wheel up from the mainspring gear, or main wheel.

Therefore, the impact of the main wheel from the break jolts the next wheel up with such force the pinion cant withstand the impact often. These are not so easy to repair if the pin breaks, it requires the removal of the pinion and the dismantling of the pinion to restore it.

So the gear or wheel, comes out, remove the pinion via a staking set. Repair this with the same steel rod size to make it perfect again. If the pin is just bent sometimes you can straighten it again with needle nose pliers for a quick fix.

Checking arbors and pivots

Meanwhile, assess the damage to the arbor of the next wheel up from the main wheel. Often it will be bent from the impact of the mainspring breaking and you would need to straighten it again if possible.

Furthermore, it is best to remove it and roll the arbor's long side on the table and see if it rolls straight.

Also, and just as important, check the skinny ends of the arbor known as the pivots. These are the skinny ends of the arbor that stick into the movements outer main brass plates.

If these are bent, the clock will not run. They need to be straight or the clock will have too much resistance in the gear train for the clock to function under the power of the new mainspring.

The teeth of the gear wheels

Lastly, inspect the teeth of the gears on both the main wheel where the spring was, and the next wheel up. Ordinarily, bent teeth are common but not as easy to correct.

Otherwise, bending back and reshaping them with a needle file sometimes works, other times the wheel needs a chunk cut out and you replace it by soldering new teeth in place.

Wooden clock case inspection

At any rate, make sure to get the movement out with no further damage to the clock case. Then check the condition of the case to be sure it does not need attention. It may need glue or nails to make it more secure as the impact of the spring breaking could loosen the boards.

To much information

On the other hand, if this is not in the realm of interest in learning about and experimenting with, please send us the movement instead. We will take care of everything for a fee. Please email a pic of what is going on to [email protected] so we can quote.

The content of this website is copyright by Clockworks and written by James Stoudenmire in year 2022

Clock Loop-End Mainspring Measuring

Measure Loop end mainsprings by width, thickness, and length. These are not always easy measurements to get, and the mainspring would need to be taken out from the clock.

It can be a frustrating puzzle to do, and a dangerous one also. But if learning clock repair or have time on the hands so to speak, here are some guidelines.

Caution !!

Always wear gloves and safety glasses when working with mainsprings. They can cut or punch the person working on the clock so please treat them with respect. It is not uncommon for the mainspring to break or shatter while working with them.

Just treat them with caution and respect while protect the hands and eyes. Be aware if a mainspring is wound up or when you stretch it way out to measure it, it has a lot of snapping power. These things can hurt when they smack the hand or fingers, or eye.

Getting the thickness and width

The items you need for this measurement are a tape measurer and a digital caliper, these are the best things to use. To get the width of the mainspring is easy, just use the digital caliper in inches and see how wide it is first.

Look on the chart below for the width column. Next is the thickness, again using the digital caliper in inch or mm. Write these two measurements down and again refer to the chart and narrow down the section even more. Now have a narrow section of the chart of sizes working with and only need the length.

Measuring the loop-end mainspring length

The length is the hardest to get the measurement on. What we do here is put the end of the spring in a vise and stretch it out. We pull the spring straight with a tape measure beside it as we unwind it.

Of course the tension of the spring is such it wants to wind back up in a violent manner.

When the spring is let go it winds back up with a snap. If there is a cat sitting by the vise and let go, the cat may not like you anymore. The length is the hardest to get but close enough is ok.

The length has not much to do with the function of the clock, only the time in which the clock will run. For example if the mainspring substantially shorter, it may not run the full 8 days.

Alternate way of measuring the length

It is possible to make the mainspring straight by just putting bends into the spring to uncoil it. Start from the end and every 6 inches put a bend with pliers in the opposite direction of the coil to make it straight.

The mainspring will eventually all be straight and then you can measure the length.

The most common size loop end mainspring for antique 1900s through 1945 American units is CML304. This size was sort of the industry standard when Seth Thomas, New Haven, Gilbert, Sessions was in full swing with the 8 day time strike units in mass production.

The content of this website is copyright by Clockworks and written by James Stoudenmire in year 2022

Loop End Clock Mainspring

To begin with, initially measure the width and align it with the width below. Subsequently, employ a micrometer to measure the thickness. Consequently, the resulting measurement will serve as an approximate length. Lastly, peruse the order list of options and select the item number corresponding to the desired mainspring, followed by clicking the "add to cart" button.

Measurements to Item #

WIDTH inch | mmTHICKNESS inch | mmLENGTH inchItem #
1/8' 3.2.010' | 0.2519'CML 245
9/64' 3.6.009' | 0.2325'CML 246
5/32' 4.009' | 0.2326'CML 247
3/16' 4.8.012' 0.331'CML 252
3/16' 4.8.016' 0.4154'CML 253
13/64' 5.0105' 0.2625 1/2'CML 254
7/32 5.6.011' 0.2824'CML 255
7/32 5.6.017' 0.4330'CML 256
1/4' 6.4.010' 0.2526'CML 257
1/4' 6.4.012' 0.3141'CML 259
1/4' 6.4.013' | 0.3324'CML 260
1/4' 6.4.016' | 0.4154'CML 261
9/32' 7.009' | 0.2330'CML 262
9/32' 7.012' | 0.327'CML 263
9/32' 7.012' | 0.330'CML 264
9/32' 7.017' 0.4348'CML 265
19/64' 7.5.015' 0.3839'CML 266
5/16' 8.009' 0.2320'CML 267
5/16' 8.009' 0.2336'CML 268
5/16 8.010' 0.2530'CML 269
5/16 8.013' 0.3324'CML 270
5/16' 8.013' 0.3330'CML 272
5/16'.013' 0.3330'CML 272
5/16' 8.015' 0.3842'CML 273
5/16' 8.016' | 0.4154'CML 274
5/16' 8.016' | 0.4172'CML 275
5/16' 8.017' | 0.4342'CML 276
5/16' 8.020' | 0.5146'CML 277
3/8' 9.5.011' 0.2851'CML 279
3/8' 9.5.013' 0.3334'CML 280
3/8' 9.5.014' 0.3648'CML 281
3/8' 9.5.014' 0.3660'CML 282
3/8 9.5.015' 0.3853'CML 283
3/8 9.5.016' 0.4160'CML 284
3/8' 9.5.017' 0.4396'CML 285
3/8' 9.5.019' 0.4848'CML 286
7/16' 11.014' 0.3672'CML 287
7/16' 11.018' | 0.4648'CML 288
7/16' 11.018' | 0.4660'CML 289
1/2' 12.7.015' | 0.3884'CML 290
1/2' 12.7.016' | 0.4166'CML 291
1/2' 12.7.018' | 0.4660'CML 292
1/2' 12.7.018' 0.4696'CML 293
6/16' 14.3.015' 0.3878'CML 294
9/16' 14.3.018' 0.4696'CML 295
5/8' 16.013' 0.3369'CML 296
5/8 16.018' 0.4696'CML 297
11/16 17.5.015' 0.38108'CML 298
11/16' 17.5.018' 0.4696'CML 299
3/4' 19.012' 0.3172'CML 300
3/4' 19.014' 0.36108'CML 301
3/4' 19.016' | 0.4178'CML 302
3/4' 19.017' | 0.43120'CML 303
3/4' 19.018' | 0.5696'CML 304
13/16' 20.6.018' | 0.4696'CML 305
7/8' 22.2.018' 0.4696'CML 306
1' 25.4.018' 0.4696'CML 307

Additional information

Weight0.25 lbs

CML 245, CML 246, CML 346, CML 247, CML 252, CML 253, CML 254, CML 255, CML 256, CML 257, CML 259, CML 260, CML 261, CML 262, CML 263, CML 264, CML 265, CML 266, CML 267, CML 268, CML 269, CML 270, CML 272, CML 273, CML 274, CML 275, CML 276, CML 277, CML 279, CML 280, CML 281, CML 282, CML 283, CML 284, CML 285, CML 286, CML 287, CML 288, CML 289, CML 290, CML 291, CML 292, CML 293, CML 294, CML 295, CML 296, CML 297, CML 298, CML 299, CML 300, CML 301, CML 302, CML 303, CML 304, CML 305, CML 306, CML 307, CML 308

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Tom maxwell
Tom maxwell
4 months ago

My loop mainspring measure 3/8 x 0.4. x 49”
Should I buy the CML 281 or 283
There appears to be enough room on the winder

Stephen Thompson
Stephen Thompson
5 months ago

Morning, How do I know which one I need for a Hapeanker Wesminster clock?
Thans, Steve

6 months ago

Im looking for the size of a seth thomas number 40 movement main springs its time only

6 months ago

I have a 1960s alarm clock called Renown Repeat Alarm made in West Germany. I think the springs maybe the alarm springs but definitely the main clock spring need replacing.
What type of springs should I order? Thank you!

Jerry Knudson
Jerry Knudson
8 months ago

My original spring is a loop end 3/4″ x .12 x 106, you 301 spring is out of stock. Do you expect more soon? Do you have a recommendation of a different spring that is in stock and would be functional?

Tony Seale
Tony Seale
1 year ago

I don’t see a measurement for diameter of the middle hole of the spring. Mine is approximately 1/8″. How do I know which spring to order.

1 year ago

Could You help me with a Loop End Mainspring which length is 55′ 3/4” and the width is 21/32” , and the thickness is approx.. 0.5 mm. I don’t see these measurements in Your list, so I wonder if you can help with one i can use. Thanking You in advance I remain, AR Carrion. Rocky.

Gary Knoth
Gary Knoth
1 year ago

Hello James.
I need to know the Diameter of the 1 inch wide .018 thick loop end spring.

1 year ago

Hello James,
I am in need of a 7mm x .43 x 30″ open loop mainspring for a vintage alarm clock. As this is unavailable, would I be better off with a 7mm x .43 x 48″, a 7mm x .30 x 27″ or possibly a 5.6mm x .43 x 30″?

Thank you

1 year ago

I’m needing a loophole spring 108” long 3/4 wide.20 or thick this would been the striker side

1 year ago

Good day Sirs, I’m in need of a Loop End Clock Mainspring and the measurements are: Length is +- 55 3/4 inches which is about 141.5 cm, the width is 5/8 inch or 21/32″inch, nd the thickness is about .3mm. To me the CLM 296 is compatible with the measurements I gave. please let Me know if it is so, s I can order one.
Thanking You in advance. I remain: Anthony R Carrion.

Mark Heenehan
Mark Heenehan
1 year ago

When ordering the mainspring and the length doesn’t match that of the one I’m replacing, do I order the longer or shorter replacement?
I’m looking at CML288 which is 48 inches. The spring from the clock is between 52-53 inches.

Harry B
2 years ago

Can just a broken sprocket that handles a pull up chain on a Zanies (miss spelled) clock be purhased?
Looking for a repair person in the Richmond/ Williamsburg VA area!

Bjorn Augustin
Bjorn Augustin
2 years ago

Dear Sirs, i have a Zenith savings clock in a wooden case that on the back plate in brass has Medor patent stamped. The main spring is broken, which size do I need?

3 years ago

I am looking for the mainspring for the pedulum wall clock Ruben Zelnick le Caire