We do not yet have much information on suspender construction. Available images tell us a good deal, but are usually frontal images which mean we know more about the frontal construction than the rear construction. As far as we know, suspenders which un English are referred to as "a pair" or twin connected straps, a least there are twin straps in front. The connection is made in the rear. Most suspenders are adjustable to fit various sizes. There was a metal clasp that allowed the length to be adjusted. I'm not sure when that first appeared. The earliest suspenders were made with button attachments.
We note Americans commonly wearing clip on suspenders by the 1930s. We are not yet sure when they first appeared. Quite a few men and many boys wore
clip-on suspenders during the 1930s. The 1939 Sears Garter Waist ad
shows ONLY clip-on suspenders for boys. The clip-on style was
obviously invented earlier.
Clip-on suspenders seem to have been originally an American invention,
but they were widely worn in Europe after World War II.
More modern suspenders have metal clasps. The attachments often forked so their were four button closures in the front. This varied somewhat in the rear. The suspender bands varied substantially in width. Perhaps HBC readers will have more detailed information about suspender construction.