Magpul made these lock-plates to help shooters know what type of magazine they are using in darkness. If your job requires you to have different type of cartridges and know which is needed in darkness, this is definitely a good choice. Available for PMAG 10/20/30 AR/M4 GEN M3 and PMAG AR 300 B GEN M3 magazines.
Price: $9.95 for a pack of 5
Single ridge is Type 1
https://www.magpul.com/products/magpul-tactile-lock-plate-type-1
Double ridge is Type 2
https://www.magpul.com/products/magpul-tactile-lock-plate-type-2
From:Magpul
