Measuring Hole End Mainsprings

September 15, 2019 8:03 am Published by Leave your thoughts

About Hole End Mainsprings

The type of springs that are contained in a brass barrel enclosure is known as Hole End Mainsprings. Measuring Hole End Mainsprings is done with the spring out of the clock movement barrel. The mainspring has to come out of the barrel to measure it.


WARNING: Wear safety glasses and gloves if working with a hole end mainsprings, they can and will be dangerous. Removal can be violent please be cautious and know there is stored power in any coiled up spring. The spring can be broken or unhooked from the center and still have much power in that spring. It can wack you and cut you and it may even shatter into pieces. Please use gloves and safety glasses when you work with coiled mainsprings.

Let us do it instead

If you choose, we have a mainspring replacement service, all you have to do is send us the entire barrel. When we get the barrel we will use special tools to safely remove the spring and measure it, and we will swap it out for the new one. Measuring Hole End Mainsprings includes these things, the thickness, the length and also the width. We will match it up with the chart to get the new one installed for you. We will ship it back the method you chose in the check out pages. If you send us the barrel please leave the mainspring in the barrel and do not remove it. This is because we need to know what way the clock mainspring gets wound inside the barrel in order to replicate this with the new one.

Measuring Hole End Mainsprings

Measuring is done to get the size 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.


Width of Hole End Mainsprings is done first. This can be measured in inches or millimeter with a digital micrometer. Then see what spring is closest in thickness and length that will be closest to the old one.


The width of the clock spring written down and the section of the chart located at this point. The width of Hole End Mainsprings is done next. This can be measured in inches or millimeter with a digital micrometer. Then see what spring is closest in length that will be closest to the old one.


The length measuring can be the hardest part of this. Close enough is sufficient for this if the spring is way too short it only means the clock will not run 8 days. It is not easy to uncoil this spring to get the length. What we end up doing is putting one end in a vise and stretching it out with a tape measure. Of course when you let go it snaps back quickly and wildly. Be sure your cat is not sitting by the vise when you let go or it will not like you anymore.


This is just the width of the inside of the clock barrel. As we said the barrel is what houses the Hole End Mainsprings. Barrel inside diameter is listed because it can help know what the spring is supposed to fit into that space.

Measuring a Hole End Mainspring

If there is no match

Sometimes there just is no match for a mainspring and it is required to use a size that is not the same. Its a tough choice at times what to substitute with in this situation. As far as the width goes its best to go skinnier one instead of wider. The spring that is too wide will make the barrel cap not go on, or stay on. The thickness is pretty important to hopefully get right. If it is too thick it will put up a fight getting in the barrel and may not want to go in. If it is too thin it may not run the clock. The length is the duration the clock will run such as 8 days or less if its too short.

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