i have snapped the little bit at top of pendulum arm on a smiths 3 key mantle clock

dean, May 2013

Dean, it sounds like you broke the suspension spring that the pendulum hangs from. You can check out the pictures on the clock parts supply houses to determine which one you need. If the wire hanger and spring are one, you will have to cut the new one to the same length as the old one.

Stevens Clocks, May 2013