Looks great! I didn't check every parameter but seems to correspond to the website I use.
http://theoreticalmachinist.com/Threads_UnifiedImperial.aspx
I know this is probably intended as a hobby assist tool, one minor suggestion is to have a nomenclature page since there are lots of abbreviations. Most people might know what they are, but many may not. Or standardize the terminology to a cut & paste reference image, attached example. Another option I often do in spreadsheets is put a more full description in a cell comment so that when you hover over, it conveys the whole definition or other useful information. Some people like this because its helpful, some people find it busy & prefer a cleaner look & a separate 'nomenclature' page. Thanks for contributing!