I find it oddly strange you are coming up w/ a metric spindle on a Carroll DH. What leads you to believe it is a Carroll DH? The number in your first picture does not match up w/ anything in the Carroll catalogs on vintagemachinery.org. Is there a Carroll logo on the DH - didn't see anything...
There are two Carroll div head brochures over on vintagemachinery.org
Every thread nose dividing head in either brochure was listed as either a 1-3/4 x 6tpi or 2-5/16 x 6tpi threaded nose. I'd say you probably have a 6tpi nose as other have said as well. There is a hole chart there as well...