you may want to try a drill blank about .003 or maybe even .005 below .156, if they are possible to find but may not be as they are usually just drill sizes which has got me wondering why I told you to use drill blanks, as it will most likely be very tight if you use a 5/32 drill and that particular hole is not as important as the belly hole will be so a small amount of play is ok and may make things work smoother. I actually use hardened gage pins of the specific size I want. The hole is really only supporting the rear end of the plug and you will find you want some play there. The belly hole is the important hole and where you want a pretty tight fit to your pin, a few thousands under, but not too sloppy as this is your locator for the whole machining of the plug. Again the hole you drill in the wood will tend to be smaller than the drill you use so you want to allow for the shrinkage. Just some food for thought. That is why the rear end of a drill may be a good choice as they tend to be a thousands or 2 smaller than the bushiness end of the drill.
here are gage pins but they are not chea, but come in any size you want. MSC will carry individual pin sizes. an example is below.
http://www1.mscdirect.com/eCommerce/...%26+Inspecting
http://www1.mscdirect.com/eCommerce/...rchandizedOk=Y
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