These magazine followers replace the often broken magazine plunger on a single stack WE 1911 magazine. They will fit 1911 GI, MEU, and other WE M1911 gas pistol magazines.
The best key to preventing broken followers is to not smack the plunger into the top of the magazine. Loading one or two BBs before drawing the BB plunger down is a good safety, just in case it slips. Alternately, it can't hurt to have a couple of extra follower parts on hand to fix something when it does break.