This replacement or spare magazine is compatible with your Enfield #1 MKIII. It is constructed of heat treated steel with injection molded mag follower and mag spring formed from chrome silicone wire. Made in the USA.
Specifications:

Caliber	303 British
Capacity	10
Finish	Blued
Model	Enfield 1-MK II
Material	Steel
Type	Detachable
Model Fit	1-MK II
Brand Fit	Enfield
Max Capacity	10