This is the 15 round Glock Gen 4 factory magazine for the Glock 22 and Glock 35 in .40 S&W.
The Gen 4 type is backwards compatible with all previous generation Glock pistols, as well as the newer Gen 5 (with the magazine catch installed in the default position).
Manufactured from hardened steel incased in Glock's trademark tough polymer these are very durable.
