A combination tool for drilling a bore and countersink for that bore includes a countersink member. The countersink member comprises a longitudinal sleeve with a first end and a second end. The sleeve contains a longitudinal bore through the sleeve from the first end to the second end sized to receive a drill bit. A radial slot through the wall of the sleeve is in communication with the longitudinal bore. The sleeve has a cutting edge connected to the first end of the sleeve. A collar containing a radial bore through its wall is slidably inserted over the sleeve. The radial bore is in communication with the radial slot of the countersink member. A fastening mechanism extends through the radial bore of the collar and slot of the countersink member to engage the drill bit inserted through the longitudinal bore of the countersink member and thus secure the drill bit, countersink member and collar relative to one another.