Acoustic Guitar Construction

I use several thousands less than the outside diameter. The 1/4-20 coarse thread inserts I use recommend a 3/8" drill bit but I find that is too loose. I'm pretty sure I use an "S" (.348) or "T" (.358). I always seem to drill a test hole first to be sure.

I purchased a few of the inserts at Ace hardware today - I'm a little worried as they were only .50 each. Might they be inferior quality compared to what the rest of you use?

Picture? Size and shape are paramount, what are they made of?

I'll get a pic. The size is just right, the amount of threads is also, I don't know what the material is, as it was not listed on the box. I t was in a section called 'furniture hardware'.
Pic to follow.

For the course thread 1/4 -20 ----- I use the fixture shown in the start of this thread to prevent blow out, the drill bit is size"O" which mnakes the inserts a snug fit which you most certainly want, that and the CA keep the insert from backing out --- I should warn once again that over tightening the neck bolts can break the insert bond and can result in all sorts of complications upon trying to remove the neck

Here's a pic. The insert material is drawn to a magnet.

Seems that should work OK. The slot looking end is a thread cutter not for a screw driver.