Features: Standard M1913 Picatinny rail configuration Lightweight glass filled nylon construction Mounting does not require alteration of AR Handguard heat shields Includes mounting hardware and ERGO LowPro Rail Covers Overall Length - 5.685 inches 14 Slots .800, 1.700, 2.700, 3.990, 4.825 Inch Hole Spacing Model Description 4750 5-slot Polymer Rail 1 Mounting Hole, 1 Slot w/Hardware 4751 10-Slot Polymer Rail 1 Mounting Hole, 1 Slot w/Hardware 4752 5-Slot X .400 Aluminum U.M.P. 2 mounting holes - Black 4753 15-Slot (6") X .400 Aluminum U.M.P 2 Mounting Holes & 1 Slot - Black 4754 10-Slot (4") X .400 Aluminum U.M.P w/ERGO Rail Covers 1 Mounting Hole & 1 Slot - Black 4755 10-Slot (4") X .400 Aluminum U.M.P w/Radiused Adapter 4756-6 14 - slot Polymer Rail 6 Mounting Holes 4757 12 inch X .400 Aluminum U.M.P Blank No Holes - Black Anodized 4760 5-Slot Ultra Light Aluminum 2 Mounting Holes - Black 4761 10-SLOT (4") X .400 Ultra Light Aluminum U.M.P w/ERGO Rail Covers 1 Mounting Hole & 1 Slot - Black 4762 15-SLOT (6") 400 Ultra Light Aluminum U.M.P w/ERGO Rail Covers 2 Mounting Hole & 1 Slot - Black 4764 8-Slot KeyMod Aluminum U.M.P 2 mounting holes - Black