There is a well-known crimping issue related to insulation diameter. Some contacts fail about 25% of the time even though the correct wire gauge is being used. There is one specification that is often ignored: insulation diameter. The term “wire gauge” has nothing to do with the insulation diameter. Wire gauge is a measurement of the diameter of the conductive center of a wire. This is often given in AWG (American Wire Gauge) or in mm². Unfortunately, several companies use different wire insulation sizes/thicknesses for the same wire gauge (the same manufacturer may also make several sizes as well). Here is a list of single conductor cables at 22AWG from fifteen different manufacturers as an example of how much variety there is in jacket diameter and jacket thickness: https://www.digikey.com/short/z97fhm Notice the “Jacket Insulation Diameter” column, it goes as small as 1.04mm to 5.84mm. This is a large range of diameters. Metal contacts can only be crimped so far and some diameters will be too large for the contact too. Let’s take a look at a physical example with part numbers for clarity.
Let’s say someone were to buy this housing, in particular, https://www.digikey.com/product-detail/en/molex/0510350600/WM17799-ND/3262406 and require 22AWG wire. One of the associated crimp contacts would be WM3312CT-ND. Luckily enough, this particular crimp has a drawing that has a minimum and maximum insulation size (here is a link to the drawing: https://www.molex.com/pdm_docs/sd/500988000_sd.pdf). Here is a blown-up picture that shows the information for insulation diameter:
This document is using mm as a base measurement.
The unfortunate situation is this: not all crimp contacts give this kind of range on their drawings or technical documentation. Manufacturers sometimes don’t keep the same information consistent for all their products. I saw a lot of examples with only a “maximum insulation diameter” given, but no notes on minimum insulation diameter. However, Molex offers a guide that has a general note on page seven: https://www.molex.com/pdm_docs/ats/TM-638000029.pdf, they say that the crimp should be able to firmly grip at least 50% of smaller insulation sizes. This does mean that some crimp contacts would have to be estimated for minimum insulation diameter, but a “hard” number is not given most of the time due to so many variations in wire (the guide also mentions that). Any manufacturer that makes crimp terminals also use insulation diameter as important measurements for determining crimp quality.