If you are building a Mk13 Mod 5 or clone, and do not have the discontinued ACIS 2.0 stock with the thumbhole, you need this adapter. Buy this and an AT folding stock, and you have what you need.
Upgrade kit for AT stock in Pale Brown. Includes thumb hold back strap, rear moldings and screws.
Note: This is for folding stocks
Accuracy Int'l (AI)
Potomac Armory