The YM SP-1 Bolt Carrier is for folks who are building or restoring a Vietnam Era SP-1 model rifle.This carrier is the original SP-1 design. The first Colt SP-1 rifles issued during Vietnam did not have a forward assist on the upper and were of the M16 style. ( Full hammer ramp, M-16 cut on bottom) So as you can see these carriers have no forward assist notches on the side. These WILL NOT WORK with your “Lightning Link”. If you want a “Lightning Link” carrier we have them. Available in Chrome, Phosphate, M-16, AR15. Please Specify.What makes Young Manufacturing AR15 bolts and bolt carriers so accurate? Check our “What makes our Bolt Carriers Better?” on our home page.