Recommended Digital Calipers for measuring parts (+ rare Clutch Test Implements.)

[Gerald Lasser]

I recently got my hands on some rare parts which are used to test LEGO parts.  They are described in the middle of an article on New Elementary as "Clutch Test Implements".  In my case, I have four of these parts in my hands:

• Stud testing part
  
• Small Towball testing part
  
• Large towball testing part
  
• Bar/clip testing part.
  

The first three have 5-digit part ID's, and the fourth one does not.  They are in a mix of uncolored ABS, Green/Dark Green ABS, and Trans-clear.  Since they have Part ID's, I was willing to make the required measurements to allow them to be added to LDraw Parts Library.

A few questions:
1) Can someone recommend a modest-priced pair of digital calipers that work well in measuring LEGO parts?  (ex: Are the Harbor Freight ones good enough?)
2) Are unreleased parts allowed in the LDraw Parts Library?
3) Are there tips to take the best and mot accurate measurements?

Thanks,
---tom

I got my digital Calipers from a discount store and they were around 10 EUR, it serves me well.

As those parts are  used for connection testing, I would compare the measurements between released parts and those test parts, i.e. stud size the same, bar size etc.?

Concerning the parts, I think they can be added, let's hear from the others.