I've been looking for a Starrett H-8 combination square for a long time. Recently, I found used one at a decent price.
Starrett-H8.jpg
That's a standard 12" combination square in the picture to show the size of the Starrett H-8. The H-8 has a 24" rule and the head is maybe 8" (I didn't measure it).
While you can get longer rules for the standard combination square heads, the size of the head limits the usefulness of those long rules.
Anyway, just wanted to pass along the picture for those people who have never seen an H-8.
Mike