hollow-type harmonic series 20-50 series from HD systems in Japan.
SHF or SHG but I failed to find exact matching model, measured all dimensions myself not to make wrong PCD holes.
probably a custom-sized one, dissembled and sold by a scrap company, 48T S3M pulley already attached when it came to me.
and from the picture, I can only guess that chinese copy company even copied naming of each model.
from the above link, you can look for model table, mine is series 20, with 50:1 reduction (which in fact 51 turns pere one turn of output)
size 20 is good for 100mm chuck(4") with a backplate.
I do not know the different between them. Do those things can't be used for rotary table. I am interested due to price is cheap. I do not know what the meaning cross roller bearing for harmonic drive. Maybe we need those two.
A crossed roller bearing (CRB) is the main support component for a harmonic drive (HD). You can buy just the key components of a HD if you want to integrate it into what you are building (eg a robot arm) with your own bearings, or you can buy a complete HD gearbox with the CRB integrated. Look up the engineering drawings for a complete gearbox on the HD web site.