HASMX 647956-00, 64795600 Trigger Valve Assembly for Dewalt Fits the following models: D51256 Type 1 Finish Nailer Kit, D51256 Type 2 Finish Nailer Kit, D51238 Type 1 Brad Nailer Kit, D51430 Type 1 - Amazon.com
Dewalt d51850 repair - YouTube
DeWalt D51850 3 1/2" Framing Nailer (Type 1) Parts and Accessories at PartsWarehouse