When installing a 3mm thick iron into a plane designed to take a 2mm thick one, the original Y-Lever sometimes isn't long enough to reach through and engage the cap iron.
The tab on this Y-lever casting is larger and the through hole smaller than the replacement Record and Clifton ones that we sell. It can therefore be filed and drilled to fit the majority of planes perfectly.
Many manufacturers intentionally use weak materials for the Y-Lever so that it will fail first if the plane is adjusted with the lever cap set too tight.
This Y-Lever casting is made from unhardened steel so it is a little more robust. Naturally this places greater onus on the user not to over-tighten the lever cap.