Hole End Mainsprings

Measuring the Hole End Mainspring

A Hole end mainspring is use when the mainspring is contained in a brass barrel.Read More »

Hole End Clock Mainspring

What is being measured below is the sizes of the new mainspring to match up to the old one.

The width is measured first and matched up to the width below, then the thickness is measured with a micrometer, then the approximate length.

So, if you match up the width first, you can then see what spring is closest in thickness and length that will be closest to the old one.

The diameter column is what the spring will fit best, in the inside diameter of the brass barrel. WARNING: Wear safety glasses and gloves if working with a hole end mainsprings, they can and will be dangerous. If you choose, we have a mainspring replacement service, all you have to do is send us the entire barrel.

Determining if the movement is worth fixing

When a hole end mainspring breaks in the barrel the impact may have caused damage in the rest of the gear train.Read More »

It is possible that the pivots that go into the outer plates have bent or the arbors bent some, its best check on this before finding a mainspring.

The length, width, and thickness would need to be measured and then you would match it up on the chart below.

Now if the mainspring has any size at all to it, it would require special tools to reinstall the hole end mainspring into the barrel.

These tools are over a hundred dollars, if the mainspring is larger then it would be very hard to put in and dangerous at the same time.

If the movement is 25-30 years old, it has lived its life anyway. A new movement would be less trouble, cheaper than a over haul, and would last another 30 years, and easier than the repair process.

If you would like to explore the new movement option rather than replacing the mainspring, Please provide the movement numbers off of the back plate of the movement itself and email this information to clockworks@clockworks.com. There is another option also, just send us the clock mainspring barrel and we will swap it out with the correct new mainspring for a fee.

Hole End Clock Mainspring

Hole End Mainspring replacement service

We can do the task of measuring and installing the mainspring if you choose to send it in. Read More »

If going with the mainspring replacement because the clock is still in good shape or out of production new, then if you choose to send the entire barrel with the mainspring in it, we can swap it out for $30.

We will take out the mainspring and measure the width / thickness and approximate length and then install the correct spring back into the barrel.

If doing this please send to Clockworks PO Box 339 Huntington MA 01050 with your contact information.

It may be best also to send us an email to clockworks@clockworks.com so we can look out for the package.

It will end up being the 30 charge, and then add the price of the mainspring as stated in the below chart, and then shipping back to you.

If you would like to send in your barrel with the broken mainspring, please fill out the form at this link so we know its coming into us.

Removing a barrel and spring

Most often the barrel with the mainspring inside of it can be removed from the clock without disassembly of the clock movements outer plates.Read More »

This can be done with a mainspring let down tool, a device that allows you to hold the tension of the mainspring with your fist rather than your precious and fragile fingers. The idea is to put the mainspring let down tool over the square post that the key is to go onto, and then move the "click" out of the way with a flat screwdriver, and slowly allow the mainspring to unwind in your fist as you control the speed of the unwind easily with your whole fist rather then the fingers with a key.

To try this with a key usually ends up being a painful experience on the fingers. You will see the click that with its tension spring that your supposed to hold back, this click is what holds the mainspring to wind in only one direction.

Of course if the mainspring is broken, there usually is no worry as there is not much tension on the mainspring to begin with, but just to be safe on the movement, its best to be sure is in the totally unwound position.


Hole End Mainsprings Measurements to item #
WIDTH inch | mm THICKNESS inch | mm LENGTH inch DIAMETER mm Item # Price
3/32" | 2.3 .007" | 0.18 18" 14 CMH 100 $6
5/32" 4 .008" | 0.2 24" 17 CMH 101 $6
5/32" 4 .011" | 0.28 26 1/2" 22 CMH 103 $6
3/16" 4.8 .009" | 0.23 24" 17 CMH 104 $6
7/32" 5.6 .008" | 0.2 26" 20 CMH 105 $9
7/32" 5.6 .0095" 0.24 24" 18 CMH 106 $9
1/4" 6.4 .011" 0.28 15 3/4" MB CMH 109 $9
1/4" 6.4 .011" 0.28 39" 26 CMH 110 $9
9/32 7 .007" 0.18 44" 19 CMH 111 $9
9/32 7 .010" 0.25 18" MB CMH 112 $9
9/32" 7 .010" 0.25 39 1/2" 25 CMH 113 $9
5/16" 8 .008" 0.2 27" 18 CMH 114 $9
5/16" 8 .010" | 0.25 28" 19 CMH 116 $9
5/16" 8 .010" | 0.25 32" 23 CMH 117 $19
5/16" 8 .010" | 0.25 39 1/2" 25 CMH 118 $9
5/16" 8 .011" | 0.28 45 1/4" 28 CMH 119 $9
5/16" 8 .015" 0.38 40" 34 CMH 120 $13
5/16" 8 .016" 0.41 54" 38 CMH 121 $14
11/32" 8.7 .013" 0.33 66" 38 CMH 122 $14
23/64" 9 .011" 0.28 45 1/4" 28 CMH 124 $14
23/64 9 .0125" 0.32 18 1/2" MB CMH 125 $12
3/8 9.5 .011" 0.28 48" 26 CMH 126 $14
3/8" 9.5 .014" 0.36 48" 32 CMH 127 $14
3/8" 9.5 .017" 0.43 54" 38 CMH 128 $14
25/64" 10 .011" 0.28 45 1/4" 28 CMH 130 $14
25/64" 10 .012" | 0.32 73" 40 CMH 131 $14
7/16" 11 .010" | 0.25 32 1/4" 22 CMH 132 $12
7/12" 11 .011" | 0.28 49" 28 CMH 135 $14
7/16" 11 .0155" | 0.4 55 1/2" 38 CMH 136 $14
15/32" 12 .010" | 0.25 39 1/2" 25 CMH 137 $14
15/32" 12 .012" 0.3 53" 32 CMH 139 $14
15/32" 12 .014" 0.36 72" 41 CMH 140 $14
15/32" 12 .013" 0.33 27" 25H CMH 141 $25
1/2" 12.7 .013" 33 60" 36 CMH 142 $15
1/2 12.7 .015" 0.38 36" 25 CMH 143 $15
1/2 12.7 .016" 0.41 65" 32 CMH 144 $15
1/2" 12.7 .018" 0.46 60" 38 CMH 145 $14
33/64" 13 .010" 0.25 39 1/2" 25 CMH 146 $14
33/64" 13 .010" 0.28 45 1/2" 28 CMH 147 $14
33/64" .012" | 0.3 53" 32 CMH 148 $14
33/64" 13 .014" | 0.36 38" 30H CMH 150 $25
33/64" 13 .022" | 0.55 28" 32H CMH 151 $25
17/32" 13.5 .010" | 0.26 72" 34 CMH 149 $19
35/64" 14 .011" | 0.28 45 1/4" 28 CMH 152 $14
35/64" 14 .011" 0.28 49" 30 CMH 153 $16
35/64" 14 .012" 0.3 61" 35 CMH 155 $19
35/64" 14 .0155" 0.4 37 1/2" 36 CMH 156 $16
35/64 14 .013" 0.33 27" 25H CMH 158 $25
35/64 14 .014" 0.36 32" 30H CMH 159 $25
9/16" 14.3 .012" 0.3 39" 28 CMH 157 $16
9/16" 14.3 .015" 0.38 42" 28 CMH 160 $16
19/32" 15 .011" 0.28 45 1/4" 28 CMH 161 $16
19/32" 15 .011" | 0.28 49" 30 CMH 162 $16
19/32" 15 .012" | 0.3 53" 32 CMH 163 $16
5/8" 16 .010" | 0.25 39 1/2" 25 CMH 164 $16
5/8" 16 .011" | 0.28 45 1/4" 28 CMH 165 $16
5/8" 16 .011" | 0.28 49" 30 CMH 166 $16
5/8" 16 .013" 0.33 78" 34 CMH 167 $19
5/8" 16 .013" 0.33 105" 47 CMH 168 $25
5/8" 16 .014" 0.36 70" 39 CMH 169 $19
5/8" 16 .016" 0.41 59" 35 CMH 170 $19
5/8 16 .0175" 0.45 43 1/2" 37 CMH 171 $15
5/8 16 .018" 0.46 41" 36H CMH 172 $29
5/8" 16 .018" 0.46 72" 40 CMH 173 $19
5/8" 16 .018" 0.46 96" 53 CMH 174 $29
43/64" 17 .010" | 0.25 72" 34 CMH 176 $19
43/64" 17 .010" | 0.25 39 1/2" 25 CMH 177 $16
43/64" 17 .011" | 0.28 45 1/4" 28 CMH 178 $16
43/64" 17 .011" | 0.28 49" 30 CMH 179 $16
43/64" 17 .018" | 0.46 54" 40 CMH 180 $16
11/16" 17.5 .012" 0.3 72" 30 CMH 181 $19
11/16" 17.5 .014" 0.36 54" 34 CMH 182 $16
45/64" 18 .018" | 0.46 44" 38H CMH 183 $29
11/16" 17.5 .018" 0.46 96" 53 CMH 184 $29
45/64" 18 .011" 0.28 45 1/4" 28 CMH 185 $29
45/64 18 .011" 0.28 49" 30 CMH 186 $16
45/64 18 .012" 0.3 53" 32 CMH 187 $19
45/64" 18 .012" 0.3 61" 35 CMH 188 $19
45/64" 18 .016" 0.41 56" 39 CMH 189 $19
45/64" 18 .016" 0.41 61 1/2" 42 CMH 190 $19
45/64" 18 .0175" | 0.44 70" 45 CMH 191 $19
45/64" 18 .019" | 0.48 47" 35 CMH 192 $15
45/64" 18 .021" | 0.53 48" 40 CMH 193 $15
3/4" 19 .009" | 0.23 72" 33 CMH 194 $25
3/4" 19 .010" 0.25 39 1/2" 25 CMH 195 $16
3/4" 19 .011" 0.28 45 1/4" 28 CMH 196 $19
3/4" 19 .011" 0.28 49" 30 CMH 197 $19
3/4" 19 .011" 0.28 50" 30 CMH 198 $19
3/4 19 .012" 0.3 53" 32 CMH 199 $19
3/4 19 .012" 0.3 61" 35 CMH 200 $19
3/4" 19 .012" 0.3 75" 35 CMH 201 $19
3/4" .012" 0.3 90" 35 CMH 202 $25
3/4" 19 .014" | 0.36 90" 35 CMH 204 $25
3/4" 19 .015" | 0.38 72" 36 CMH 205 $25
3/4" 19 .0155" | 0.4 53 1/2" 37 CMH 206 $19
3/4" 19 .016" 0.41 53" 38H CMH 208 $29
3/4" 19 .016" 0.41 56" 39 CMH 209 $19
3/4" 19 .016" 0.41 60" 38 CMH 210 $19
3/4" 19 .017" 0.43 44" 35 CMH 211 $19
3/4 19 .017" 0.43 45" 36H CMH 212 $29
3/4 19 .0175" 0.44 70" 45 CMH 213 $19
3/4" 19 .018" 0.46 96" 53 CMH 214 $29
3/4" 19 .019" 0.48 68 1/2" 45 CMH 215 $19
25/32" 20 .011" | 0.28 49" 30 CMH 217 $19
25/32" 20 .012" | 0.3 53" 32 CMH 218 $19
25/32" 20 .012" | 0.3 61" 35 CMH 219 $19
25/32" 20 .0155" | 0.4 53" 38 CMH 220 $19
25/32" 20 .016" | 0.41 53" 38H CMH 221 $35
25/32" 20 .0175" 0.44 70" 45 CMH 222 $19
25/32" 20 .018" 0.46 76 1/2" 48 CMH 223 $22
53/64" 21 .011" 0.28 45 1/4" 28 CMH 224 $19
53/64" 21 .011" 0.28 49" 30 CMH 225 $19
53/64 21 .012" 0.3 53" 32 CMH 226 $19
53/64 21 .012" 0.3 61" 35 CMH 227 $19
53/64" 21 .0125" 0.32 67" 38 CMH 228 $19
53/64" 21 .015" 0.38 100" 50H CMH 229 $37
7/8" 22.2 .011" 0.28 49" 30 CMH 230 $16
7/8" 22.2 .012" | 0.3 53" 32 CMH 231 $19
7/8" 22.2 .012" | 0.3 61" 35 CMH 232 $19
7/8" 22.2 .0125" | 0.32 67" 38 CMH 233 $25
7/8" 22.2 .013" | 0.33 72" 33 CMH 234 $25
7/8" 22.2 .0155" | 0.4 50" 37 CMH 235 $19
7/8" 22.2 .0175" 0.44 70" 45 CMH 236 $19
7/8" 22.2 .018" 0.46 84" 49 CMH 237 $29
7/8" 22.2 .018" 0.46 96" 53 CMH 228 $29
7/8" 22.2 .0195" 0.5 56" 42 CMH 239 $19
61/64 24 .0175" 0.44 70" 45 CMH 240 $25
61/64 24 .018" 0.46 76 1/2" 48 CMH 241 $25
61/64" 24 .018" 0.46 80 1/2" 50 CMH 242 $25
63/64" 25 .018" 0.46 78 1/2" 49 CMH 243 $25
1" 25.4 .018" 0.46 96" 53 CMH 244 $29