Leapers, Inc. - UTG Model 4/15 Quad Rail, Fits AR Rifles, Carbine Length, with Front Extension, Black MTU015 The UTG pro Model 4/15 Extended carbine length drop-in quad rail fits model 4/15 carbines with rails extending beyond front sight. It has picatinny rails with 19 top slots" 23 bottom slots and 25 left/right slots.