I have worked with antique jewelry from time to time and the length
of the five links in a cufflink usually measure between 10mm to 13mm
The bars or buttons will vary widely with one side usually being
smaller. The smaller side is the side that passes through the cuff
while the larger is worn to the out side for show. The smaller side
have been any where from 10mm to 15mm depending in the shirt maker.
Unfortunately it seems there was no standard in the 1890s with each
shirt often being custom tailored. Check with a men's department and
see what is a standard for tailoring now and that maybe your best bet
on getting a measurement.
Associate Editor / Art Jewelry magazine
21027 Crossroads Circle / Waukesha WI 53187-1612