There is a 6R graduation Edward, I just don't know if it's available on the 24" combination blade. Every Starrett graduation is not available on every Starrett scale/blade.
OK here we go...the 6R on the CB24-6R is 1/10" top & bottom on one side and 1/50" on top & bottom on the other side of the scale.
The 4R on the CB24-4R is 1/8" top, 1/16" bottom on one side and 1/32" on top, 1/64" bottom on the other side.
I believe the blade used in the 4" double square is the same as the blade for the 4" combination square. Same thing for the 6" double & combination. The 4" blade is a little narrower and a little thinner compared to the 6".
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