High Speed Steel Standard Hand Plug Tap: 1/4-28 thread with 4 Flutes. Used for mounting accelerometers. It is advisable to first use a “Plug Style“ tap to facilitate cutting the threads. Once the plug style tap has bottomed out, back off and thread using the bottom tap. F.Y.I.: more flutes provide a greater number of cutting teeth. The tougher the material, the better it is to have more chamfered threads cutting. The max is normally 4 flutes. Cheaper taps with fewer flutes and cutting teeth can result in premature dulling and breaking.