Just want to let everyone know that I have had a few reports about the threads on my plugs being a little tight. I check every base with a go-no go gage set to be sure they are correctly sized. The trouble might be from cheap taps. If you run into that trouble try buying a good quality tap made in the USA, Poland, Japan, or Germany. As they can be expensive and may only be used a few times, or you already purchased the cheaper tap, try bumping up the tap drill one size and see if that eases the fit.
I have found some good taps in 6-56 (Japan) and 1/4-32 (USA). They are available on the website. I have my eyes pealed for 8 and 10 - 40. If I can find them for a reasonable price I will get them up also.