Type 1 SMLE magazine: Introduced with the Mk1 SMLE. Hinged front feed lip, link loop front of case, Case, platform, auxiliary spring all un-numbered
Type 2 SMLE magazine: Introduced with the Mk1* SMLE. Hinged front feed lip, no link loop, deeper at front to help charger loading, new type of auxiliary spring, same platform as type 1 so un-numbered, case & aux spring stamped with 2.
Type 3 SMLE magazine: Hinged front feed lip, No link loop, conversion of types 1 & 2 for MkVII ammo, left feed lip cut out & a new spring steel lip riveted in place, new type of auxiliary spring, platform modified to clear new LH lip, case & auxiliary spring stamped 3, platform stamped 2
Type 4 SMLE magazine: New magazine for MkVII ammo, no hinged front feed lip, no ling loop, new type of auxiliary spring, new platform, case & auxiliary spring stamped 4, platform 3.
Only Type 3 & 4 have the small spring steel bit riveted to bottom of the back rib.