Most people think of snap cufflinks from the 1920's as being all the same. Kum-A-Part was by far the largest manufacturer of this type of cufflinks. Mother of pearl and engine turned base metal were the most prominent types. Snap cufflinks were the rage for the period from the 1910's - early 1930's. They eventually fell out of favor as the snap mechanism would often fail or loosen, causing the link to come undone, or worse, to fall out, leaving 3 or less sides. In order to combat this problem, manufacturers of this period modified the simple snap design. Some of the modifications are as follows: Combination double sided and snap type: 2 button openings. I call these "Valet" cufflinks as they are physically impossible to open and close by yourself with one hand. You need a valet to help you put them on. In order to open them, you have to lift up the buttons on each underside of the cufflink. Very, very rare. One of the biggest problems with snap cufflinks is they unsnap when wearing if pressure is exerted on them. In order to remedy this, manufacturers devised the "Spool" link, where there is a solid bar. Somewhat rare, I really prefer this type. They wear well and sit nice on your french cuffs. Concerned about loosing a side if your snappers become undone, manufacturers created a way to hold them together in another method. These are very, very rare. I only have these two pairs in my collection and have only seen a few other pairs in all my collecting days. The rarest pairs in my snapper collection. The elusive side-opening pair. These are opened by pushing in on a side button (left) or turning the side button clockwise (right). I have never seen another pair like these, ever. I wonder if these pairs were prototypes not released to the public. From the 1950's, pairs of cufflinks connected by an expandable chain I got tons more of unique and rare closures. I'll save them for later. Better yet, when you are in Wilmington, DE stop by and I'll show you them in person. Over a glass of wine, of course.