Compatible with all MDT JAE Chassis models, and extends length of pull (LOP) by 1/4" per spacer. Using multiple spacers may require longer bolts, see below for information on bolt lengths. G4 Model Chassis: 1/4 - 20 x 1.50" Socket Head Cap Screws (0 to 2 Spacers)1/4 - 20 x 2.00" Socket Head Cap Screws (3 to 4 Spacers)1/4 - 20 x 2.50" Socket Head Cap Screws (5 to 6 Spacers)PRE-G4 Chassis (Original):1/4 - 20 x 1.75" Socket Head Cap Screws (0 to 2 Spacers)1/4 - 20 x 2.25" Socket Head Cap Screws (3 to 4 Spacers)1/4 - 20 x 3.25" Socket Head Cap Screws (5 to 6 Spacers) MDT JAE Buttstock Spacer 105202-BLK