Size of Hole for 1/8-27 NPT Brass Plugs

[indieFan]

I'm designing a piece of tooling that will require brass plugs to be put into it. I'm going to use plugs that will sit flush with the edge of the fixture. I've ordered the 1/8-27 NPT brass plugs, but I'm not sure what size hole I've got to drill for the tap. If you can help me out, I'd appreciate it.

Thanks,
indieFan

[Hunter]

The tap drill size for 1/8-27 NPT is a Q which is 0.332". If you need the plugs to sit flush you'll have to experiment with your plugs a little. To get a tight fit on a pipe thread different plugs won't all end up at the same depth, so you'll have to adjust your tap depth for a specific plug if its that important. Or just counterbore the hole.

[Gdeaver]

There are Hex socket plugs that may be better for a flush application. I've seen them used mostly on gas heating equipment and they are usually galvanized steel.