This is an original knob for a vintage Keuffel & Esser Co drafting table, it's just under 2 1/2" wide and almost 1" thick. They are 1/4-20 threaded. I will also include the vintage bolts.  I have two available for sale, this listing is for one knob. Buy two and save 10%. If you are missing one, this is your chance to get a replacement as they are very HARD TO FIND! Trust me, I looked.  Personally I'd buy both just in case you lose another!