Any thoughts on why recently acquired Slingerland 12" and 13" toms that mount with no problem on a Set-O-Matic post are difficult to mount on the 14 arms that I own among seven Super Set-O-Matic units?

It took almost an hour of mixing and matching to jury-rig a unit in which both arms would accept a tom. I realize that the arms are all the same (basically single tom mounts), but I was hoping to avoid having to adjust one that was dialed in for a starboard-side 13" tom. No such luck: Only one of my SSOM arms worked with the "new" 12" tom on the port side and only a handful worked with the 13". In other words, more than half of the arms that I own do not work with either of these new drums.

I realize that the SSOM unit wasn't developed until the mid- to late-1970s, but I haven't had problems installing early 70s toms on these units until now.

I'm counting my lucky stars that I tested this at home instead of at the gig.

Thanks,

Al