If you want to build an AEG (electric) gun ground up, with your own metal body and your choice of front and back end, this package includes all those little parts to make the whole thing fit together!
All of the necessary gubbins that go into a G&P AR metal body. Including such lustrous things as the bolt handle, dust cover, fire selector. Indeed, pretty much everything you need for an M4 metal body except the body itself, gearbox and motor.
A handy buy for someone building an AEG from the ground up or just looking to overhaul the rusted do-dads on your aged AR.