Loop End Mainsprings

With the mainspring out of the movement, you will need a micrometer and a tape measure.

First thing measured is the width, and 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.

The length is not easy to measure, approximate is still good.

Even if the replacement spring is not the exact same length, the clock will have no difference in timekeeping, it would only be the duration of run time altered.

When a loop end mainspring breaks the impact may have caused damage in the rest of the gear train.

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.

We offer a repair service with the best equipment for those that do not want to be bothered with the repair.

Loop End Mainspring

A loop end mainspring is the kind of spring that you can see, it is not in a container, in other words.

This spring would have a loop on the outer end of the spiral that attaches to the movement arbor.

The old mainspring comes out and then measure the width, thickness, and approximate length.

The movement needs to be dis-assembled for the old mainspring to come out.

If you choose not to do this, you can also send the movement in for repair and mainsprings replaced.

Loop End Mainsprings Measurements to item #

WIDTH inch | mm THICKNESS inch | mm LENGTH inch Item # Price
1/8" 3.2 .010" | 0.25 19" CML 245 $9
9/64" 3.6 .009" | 0.23 25" CML 246 $9
5/32" 4 .009" | 0.23 26" CML 247 $9
3/16" 4.8 .012" 0.3 31" CML 252 $11
3/16" 4.8 .016" 0.41 54" CML 253 $11
13/64" 5 .0105" 0.26 25 1/2" CML 254 $11
7/32 5.6 .011" 0.28 24" CML 255 $11
7/32 5.6 .017" 0.43 30" CML 256 $11
1/4" 6.4 .010" 0.25 26" CML 257 $11
1/4" 6.4 .012" 0.31 41" CML 259 $11
1/4" 6.4 .013" | 0.33 24" CML 260 $13
1/4" 6.4 .016" | 0.41 54" CML 261 $13
9/32" 7 .009" | 0.23 30" CML 262 $13
9/32" 7 .012" | 0.3 27" CML 263 $13
9/32" 7 .012" | 0.3 30" CML 264 $13
9/32" 7 .017" 0.43 48" CML 265 $13
19/64" 7.5 .015" 0.38 39" CML 266 $13
5/16" 8 .009" 0.23 20" CML 267 $13
5/16" 8 .009" 0.23 36" CML 268 $13
5/16 8 .010" 0.25 30" CML 269 $13
5/16 8 .013" 0.33 24" CML 270 $13
5/16" 8 .013" 0.33 30" CML 272 $13
5/16" .013" 0.33 30" CML 272 $13
5/16" 8 .015" 0.38 42" CML 273 $13
5/16" 8 .016" | 0.41 54" CML 274 $15
5/16" 8 .016" | 0.41 72" CML 275 $27
5/16" 8 .017" | 0.43 42" CML 276 $12
5/16" 8 .020" | 0.51 46" CML 277 $15
3/8" 9.5 .011" 0.28 51" CML 279 $15
3/8" 9.5 .013" 0.33 34" CML 280 $15
3/8" 9.5 .014" 0.36 48" CML 281 $15
3/8" 9.5 .014" 0.36 60" CML 282 $15
3/8 9.5 .015" 0.38 53" CML 283 $15
3/8 9.5 .016" 0.41 60" CML 284 $15
3/8" 9.5 .017" 0.43 96" CML 285 $26
3/8" 9.5 .019" 0.48 48" CML 286 $15
7/16" 11 .014" 0.36 72" CML 287 $15
7/16" 11 .018" | 0.46 48" CML 288 $15
7/16" 11 .018" | 0.46 60" CML 289 $15
1/2" 12.7 .015" | 0.38 84" CML 290 $20
1/2" 12.7 .016" | 0.41 66" CML 291 $17
1/2" 12.7 .018" | 0.46 60" CML 292 $17
1/2" 12.7 .018" 0.46 96" CML 293 $26
6/16" 14.3 .015" 0.38 78" CML 294 $20
9/16" 14.3 .018" 0.46 96" CML 295 $25
5/8" 16 .013" 0.33 69" CML 296 $25
5/8 16 .018" 0.46 96" CML 297 $16
11/16 17.5 .015" 0.38 108" CML 298 $29
11/16" 17.5 .018" 0.46 96" CML 299 $29
3/4" 19 .012" 0.31 72" CML 300 $29
3/4" 19 .014" 0.36 108" CML 301 $29
3/4" 19 .016" | 0.41 78" CML 302 $20
3/4" 19 .017" | 0.43 120" CML 303 $29
3/4" 19 .018" | 0.56 96" CML 304 $16
13/16" 20.6 .018" | 0.46 96" CML 305 $49
7/8" 22.2 .018" 0.46 96" CML 306 $39
1" 25.4 .018" 0.46 96" CML 307 $39