Back in the day with all of the many sizes of aluminum arrow shafts it was easy to get just the right spine to match any bow or broadhead. Most broadheads were lighter then and it was common to find that if a 2020 would be too stiff for a bow and broadhead combination, the 1920 would be just right. The same for those that found 2016s to be slightly too stiff, simply go to 1918s. No need to play the guessing game with an extra long shaft and keep whittling it down until it flew. 3/4" clearance was a standard idea, as were Zwicky, Bear and Ben Pearson broadheads. Today, we still have that option with matching the shaft to the draw/broadhead/bow situation in wood shafts. We hear a lot about how the days of great wood arrows like Acme are gone forever, but there are three suppliers of wood shafts that I believe have surpassed Acme. My standard arrow is a 1918 for most of my bows, one bow I shoot 1920s and on one bow I shoot 1818s. I do switch to woods at times when I start thinking about how I will not ever be able to replace my aluminum shafts. My stash of aluminum shafts are not for sale.