This is the Strike Industries ARLRSKPRO, a comprehensive AR-15 lower Receiver spring replacement kit. The kit provides you with 9 essential springs often replaced or misplaced when constructing stripped AR-15 lower receivers. The 9-piece kit includes springs for bolt catch, disconnector, buffer retainer, trigger, hammer, magazine catch, selector, and two detents. A perfect pick for your AR-15 assembling needs.