The Enhanced Lower parts kit offers a convenient upgrade package for the AR-15 for those looking for a complete Strike Industries solution for new builds, or to update their plain jane AR. This kit includes all the basics that you will need to build out your AR (minus grip), but with Strike Industries Enhanced lower parts where applicable.Package includes:SPRINGS: 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.PINS: Enhanced Bolt Catch - features improved grip surfaces and angles Enhanced Magazine Catch Enhanced 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 60-90deg 3-in-1 Selector Shaft - with Screws/li> 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 componentsFeatures- Includes SI's signature Enhanced Lower Parts (AR-EBC, AR-EMC, AR-EPTP, & AR-HS-60/90-3in1)- SI's Trigger spring provide a consistent 4 1/2 to 5 1/2 lbs trigger pull with our fire control group