Leica Lens Hood Summilux-M 21mm ASPH.
This is the dedicated push-on cap for the lens hood which is originally supplied with the 21mm f/1.4 Summilux-M Aspherical lens, and is offered here as a replacement for a lost or damaged cap.
This cap is specifically made for the proprietary hood for the 21mm f/1.4 Summilux, and isn't for use upon any other hood. It has an embossed Leica logo on the front. The 21mm Summilux hood accepts Series VIII filters on the inner side (lens side) of the hood.