not sure if the following will help:
The standard length chart indicates length for maltby hybrids, and the Hybrid chart indicates length for the FDI heads. The #4 FDI is 246 grams is the same as the STi-2 iron head (#4) and pretty close to the PTM (#4).
The trimming chart indicates what the manufacturer would recommend (which coincides with the links to the two charts above).
It’s seldom I follow the exact trim code as I shoot for a particular cpm, often times I’m between flexes so instead of 1/2″, I might trim 1/4″ or 3/8″. In addition I normally build to MOI specifications, so my standard lengths are based on 3/8″ intervals.
Of course, I can be a bit anal!
Hope this helps.
Thanks for your quick response. The article was super helpful. One question through regarding the IR27 tipping guides, which seem to be counter-intuitive to the article content. If you base the tipping instructions off of the head weight, which makes total sense, why does IR27 reference length not club head (2, 3, etc)?