This is the extended Glock 19 Gen 4 factory magazine, with a +2 extension to give 17 round capacity to the Glock 19 compact.
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 encased in Glock's trademark tough polymer these are very durable.