The Flat mount ABR (Patented) will directly bolt on to the MPA BA, Hybrid, ESR and Bergara Premier Competition with an MPA Chassis models and it is supplied with the proper length bolts (and the short dowels). The two step aluminum cross stud for the monopod (called the Bag Rider Barrel) will be used for the longer front mounting bolt. While ABR is opened start the two supplied bolts with your fingers - finish tightening with an Allen wrench. DO NOT take apart the ABR. There is a short 1/4-20 bolt installed in the ABR that has to be removed for applications other than the MPA chassis. A new 'Quick adjustment' thread option (Coarse thread) is available for PRS, Hunting - use requires Hardened Dowels ELR & V. Unlike other options - the ABR with linear bearing provides the ultimate in smoothness with zero wobble. The ABR has about .95 of travel with the short dowel and 1.48 with the long dowel. Made in the USA from American 6061 Alum and finished with Class II Anodizing they are less than 14oz. Caliber restrictions for dowels: .338 and smaller will use the Standard dowels .33XC and larger will need the Hardened Dowels PRS use requires Hardened Dowels Direct Bolt On application: MPA BA: Competition, Hybrid, ESR, Evolution, Lite, Ultra Lite, and Bergara Premier - Short Dowels (The Long dowels will require milling) Modifications Required: ORYX Chassis - (Long Dowels) If your chassis does not have the slot for the M-Lok - we suggest to reduce height added to the rear stock - that you directly bolted onto the lower stock without adding a picatinny rail. Since machining is required either way to add the bolt holes the Flat Mount designed ABR has two small slots and counter bored areas for the bolt heads to be recessed. XYLO chassis - (Short Dowels) The lower rider (part of the stock) will need to have bolt holes added to mount the Flat Mount ABR (which already has 2 small counter sunk slots). MPA - to fit the Longer dowels the rear dowel will have to pass into the stock so milling a hole is required. Sig Cross - The rear stock must be modified to fit the ABR and the holes milled in the ABR to clear 10/24 bolts. The LOP plate must be modified to clear rear dowel. MPA Matrix - Custom installation (milling required) Tubb Rifles - (Long Dowels) Daniel Defense Delta 5 Pro APAC Chassis - from JP Rifles Bergara BMP Please note that this product does not fit all MPA stocks. Will not work with Modular Weight Tuning Kit. Non-Affiliation Disclaimer. We are not affiliated, associated, authorized, endorsed by, or in any way officially connected with the MasterPiece Arms Holding Company brand.