SI Enhanced AR-15 Lower Parts Kit (Builders Kit)

In stock

The Strike Industries Enhanced AR-15 Lower Parts Kit offers a convenient upgrade package for the AR15 and those looking for a complete Strike solution for new builds, or to update their plain jane AR.

This is called the Builders Kit as it includes all the essential parts needed to complete your build. It does not include the pistol grip or mil-spec trigger parts because we understand that builders may want to include a pistol grip or drop-in trigger of their own choice.

Below you'll find a complete breakdown of all the parts this kit comes with including our Strike Enhanced parts which provide better looks and higher function than an average LPK.

COMPATIBILITY: AR-15 and AR-9 Mil-Spec lower receivers

NOT COMPATIBLE: AR-10: Bolt Catch, Bolt Catch Roll Pin, Pivot Pin and Takedown Pin are not compatible with AR-10 lower receivers.



  • Bolt Catch Spring - easily confused with the disconnector spring; disconnector spring is tapered though.
  • Buffer Retainer Spring - second largest coil type spring in the kit.
  • Disconnector Spring – slightly larger than bolt-catch spring, identifiable because one end is a little bit wide than the other.
  • Hammer Spring - largest of all the springs. 
  • Magazine Catch Spring - this is the largest coil spring in the kit.
  • Pivot Detent Spring - same as the takedown detent spring, so there are two in a kit.
  • Selector Spring - similar to the takedown and pivot detent springs, but larger diameter; there will only be one of these.
  • Takedown Detent Spring - same as the pivot detent spring, so there are two in a kit.
  • Trigger Spring - the smaller of the two largest springs.


  • Enhanced Bolt Catch  - features improved grip surfaces and angles
  • Strike Magazine Catch 
  • Strike Magazine Catch Button - features improved grip surface
  • Enhanced Pivot Pin - longer of the two large pins.
  • Enhanced Takedown Pin - smaller of the two large pins.
  • SI Selector Lever - 2 included in package
  • SI Selector End Plate
  • SI 60-90° 3-in-1 Selector Shaft - with screws
  • Bolt Catch Plunger – mushroom shaped pin
  • Bolt Catch Roll Pin - smaller of the two roll pins.
  • Hammer Pin – solid pin with machined grooves; can be inserted from either side.
  • Pivot Detent - same as takedown detent; both sides usually rounded or semi-conical.
  • Selector Detent - one end is flat, the other pointed/semi-conical.
  • Takedown Detent - same as pivot detent; both sides usually rounded.
  • Trigger Pin - same as hammer pin; can be inserted from either side.
  • Buffer Retainer  – large hollow barrel with small pin protruding from the top
  • ** Highlighted parts are SI exclusive ENHANCED components

- Includes SI's signature Enhanced Lower Parts (AR-EBC, AR-SMC, AR-EPTP, & AR-HS-60/90-3in1)
- SI's Trigger Springs provide a consistent and smooth 4 ½ to 5 ½ lbs trigger pull with our fire control group

DISCLAIMER: Please note that due to the compact design of the Strike PDW Stock and PDW Stabilizer, the SI Extended, Shift & Ultra Light Pivot/Takedown Pins, as well as other possible extended pin sets on the market, may bind and or will not clear the slide rods.

WARNING: This product contains chemicals known to the State of California to cause cancer and birth defects or other reproductive harm. For more information: