Gun Nuts Pro Line Fire Control Group Lower Parts Kit - The Schmid Tool Gun Nuts line of AR-15 Parts was crafted by Schmid Tools, a company that has been producing fire control groups and lower parts kits for military contracts since 1980. Schmid Tool knows exactly what goes into making every part perfect. The Schmid Tools Pro line is an entry level, cost effective, mil equivalent single stage for builder kits. Includes: Trigger Hammer Disconnect Hammer Spring Trigger Spring Disconnect Spring Hammer Pin Trigger Pin Finish: Manganese Phosphate Trigger Type: Single Stage Pin Size: Small (.154in)