When inspecting a hole, what gauge would you use to check diameter?

• A. Dial indicator.
• B. Go/no-go gauge (bore gauge) or plug gauge.
• C. Gage block.
• D. Face mill.

Answer: (B)

When checking the size of an internal feature like a hole, you need a tool designed to measure inside dimensions. A go/no-go gauge or plug gauge is built for this purpose: the go gauge should fit the hole if the diameter is at or below the lower tolerance limit, and the no-go gauge should not fit if the hole is within tolerance, giving a quick pass/fail check. A bore gauge, which can be used to take a precise internal measurement (often read on a dial or with a digital readout), is also appropriate for confirming the exact diameter.

Dial indicators measure displacement and runout, not the actual hole size, so they’re not the primary tool for verifying diameter. Gage blocks are used to set up or calibrate measurement devices and to form reference lengths, not to measure a hole directly. A face mill is a cutting tool, not a measuring instrument, so it won’t be used for inspection.

So for checking diameter, go/no-go gauges or a bore gauge are the correct choices because they directly assess the internal dimension against the specified tolerance.