My pleasure.

I'm not aware of anything similar for Sapim or Wheelsmith. I believe these nipples were cut and photographed by Roger Musson for his book, and he uses DT exclusively.

I really didn't intend to start a contentious debate about which way to round spoke lengths, and in any case I certainly am not recommending rounding down more than a millimeter from the calculated length for 12mm nipples.

Here's more on the subject from Roger Musson in his book Wheelbuilding, 4th ed., and my own experience pretty much reflects his advice. The photos he refers to are those in my post six posts up (Figure 59 from his book).

Spokes are generally manufactured in 1mm increments but many stores only stock even sizes, and some spokes are only made in 2mm increments. When using the spoke length calculator I always treat the resulting spoke sizes as maximums, there are however other considerations and this relates to the length of nipple used.

My spoke length calculator aims to calculate a spoke length such that the threaded end of the spoke lies flush with the bottom of the slot in the nipple - about 1mm below the top surface of the nipple. Rounding the spoke length up or down is based on the size of the nipple being used.

The following discussion is applicable to DT spokes; I'm not sure if the same applies to other brands.

For illustration purposes I've produced some cross sections of 16, 14, and 12mm DT nipples shown in Figure 59. The ruler at the top is in 1mm increments. All the nipples were gently screwed down until the threads bottomed out. Once the threads bottom out the nipple becomes tighter to turn, it will easily tighten with the wrench but the spoke will be deforming the threads in the nipple and whilst generally okay I always try to avoid this by selecting the correct length spoke.

12mm nipples

This is the most common size and accounts for the vast majority of wheels I build. The only time I use something longer is on the Mavic UST rims where a longer nipple is required due to the special eyelet design (Mavic recommend 16mm but I use 14mm).

When using 12mm nipples my ideal length is when the spoke is flush with the bottom of the slot in the nipple which is about 1mm below the top surface of the nipple (this is the length given by the spoke calculator). As you can see from the photo the spoke can easily screw through an extra 2mm (1mm above the top surface) so for spoke length purposes there is plenty of leeway in selecting a suitable length. With the ideal length at the bottom of the nipple slot you can go +/- 1mm. You could go +2mm but you will encounter the nipple bottoming out (emphasis mine - Stan). I wouldn't go -2mm because you are getting too low a thread engagement and also the shorter spokes will be more problematic when lacing/tensioning because you will be getting tight spokes too early in the build process unless you modify your nipple driver accordingly.

For example if using standard 12mm nipples and I calculated 264.6mm it would be okay to go with 265 or 264 but with a calculated 264.5 I'd be going with 264 but with the 12mm nipple it's not critical.

14mm nipples

The spoke in the bottomed out nipple lies flush with the top surface of the nipple. The spoke calculator will provide a length to the bottom of the nipple slot so you must subtract 1mm to give the ideal length which gives the option of then selecting spokes in the range plus/minus 1mm without fear of encountering the nipple bottoming out.

16mm nipples

The spoke in the bottomed out nipple lies flush with the bottom of the nipple slot so this is the absolute maximum length - do not go longer. This would be the length that the spoke calculator gives you so you need to modify this length by subtracting 2mm to give the ideal length with the option of then selecting spokes in the range plus/minus 1mm.

The DT Swiss spoke length calculator automatically subtracts 4mm if you specify a 16mm nipple and subtracts 2mm if you specify a 14mm nipple, both of which I find excessive compensations.