Introduction
The mainspring is the power source for spring-driven clocks. Choosing the wrong thickness, length, or barrel size can cause weak running, overwinding issues, or serious movement damage. This guide explains how to choose the correct mainspring for your mechanical clock.
Understanding What a Mainspring Does
Stores and releases energy
The mainspring powers the time, strike, or chime train depending on the barrel.
Must match the barrel size
Incorrect width or thickness prevents proper winding or causes binding.
Affects run time and power
Spring strength determines how consistently the clock runs over its cycle.
How to Identify the Correct Mainspring Dimensions
Measure the spring width
Width must match the barrel interior. Even small differences cause binding.
Measure the spring thickness
Thickness determines power. Too thick overstresses the movement; too thin causes weak running.
Measure the spring length
Length determines run time. Too long will not fit; too short reduces duration.
Matching the Mainspring to the Barrel
Check the barrel interior diameter
The spring must fit comfortably without excessive compression.
Check the arbor hook style
Some springs use holes; others use loops or T-ends.
Check the barrel hook style
The outer end must match the barrel’s retaining hook.
Common Mainspring End Styles
Hole-end springs
Used in many American clocks. The arbor engages a punched hole.
Loop-end springs
Common on European clocks. The arbor engages a formed loop.
T-end springs
Used on some barrel-driven clocks. The T-end locks into a slot.
Choosing the Correct Spring Strength
Match the original thickness
Thickness directly affects power. Never guess or “upgrade.”
Match the movement type
Time-only clocks use lighter springs; strike and chime trains require stronger ones.
Do not exceed manufacturer specifications
Overpowered springs cause bent arbors, worn pivots, and plate damage.
Common Mistakes When Choosing a Mainspring
Choosing by appearance instead of measurement
Springs that look similar may differ in width, thickness, or length.
Using a thicker spring for “more power”
This is the #1 cause of movement damage.
Ignoring end style compatibility
Incorrect end styles prevent the spring from engaging the arbor or barrel.
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FAQs
How do I know what mainspring my clock needs?
Measure the original spring’s width, thickness, and length or match the movement specifications.
Can I use a thicker mainspring for more power?
No. Thicker springs damage the movement and do not improve performance.
What happens if the mainspring is too long?
It will not fit the barrel and may bind or fail to wind fully.
Do all clocks use the same end style?
No. Hole-end, loop-end, and T-end springs are not interchangeable.
Why does my clock run weak after replacing the mainspring?
The replacement may be too thin, too short, or incorrectly matched to the barrel.
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