Part of the challenge of selecting a combo kit is figuring out which nail guns you need. Two issues to consider here are nail length and gauge. Surely, you’ll want to drive a range of nail lengths, just as you would with ordinary hand-nailing, to create solid connections. A 15- or 16-gauge brad nailer will provide you the sturdiest nails in lengths up to 2-1⁄2″, but they leave the biggest hole behind. Eighteen-gauge brad nailers also accept a wide range of nail sizes up to 2″. The thinner nails are ideal for general woodworking and trim jobs, and their signature is more discreet. For ultra-fine work, where appearance matters more than brute strength, a 23-gauge pin nailer is ideal. Pin-hole sized dots are their only trace.