WWII Sparks-Whithington Thompson M1928 or M1A1 Magazine

This is a WWII 20 round stick magazine for the Thompson M1928 or M1A1 Machine guns. This variant was made Sparks-Whithington who produced batches during WWII without any identifing makers marks or codes. Several makers, Colt, AO and Sparks- Withington produced similar "blank" magazines without any markings. Identifing who made which one is done using several checks; the hole spacing and follower design. Sparks-Whithington spaced thier viewing holes 0.20 inches from the back of the body to the middle of the holes, and there should be be a small hole on the back of follower.