Mainspring

There are basically two types of clock mainsprings. They are hole end and loop end. The hole end is used inside a barrel and has a "D" or oval shaped hole at one end of the mainspring. This allows the mainspring to be attached to a fixed point such as a barrel hook. The loop end has either an oval or round closed end to allow a post or other fixed movement stem to be used as the "anchor" of the mainspring. On smaller loop end mainsprings, the loop end can be open.