Hanging Clamps, Plan Sticks, Plan Holders, Drawing Clamps, Blueprint Clamps, whatever you want to call them, they're all the same thing! Safco and Mayline are the two biggest manufacturers of these products. They make them from rigid aluminum and the two brands are interchangeable. There was a company long ago that manufactured them under the name of PlanHold, but Safco purchased that company and still makes the "Print Lock Plan Hold" hanging clamps.
If you want to know how hanging clamps work, first you should understand that they are made and sold in different lengths. They are made in standard size lengths of 18", 24" 30", 36" and 42". You buy the size (length) of clamp you want, depending on the size of drawings or documents you plan to clamp. For example, if you have a 24"x36" drawing, you'll probably want to buy 24" clamps since you'll clamp the left bound edge of your drawing set which is 24" and it'll fit the clamp perfectly. The clamp part (the part that actually touches and clamps the drawings) is the length as most clamps have a little bit of overhang on each end, this is so the clamps can be hung in or on a blueprint rack or stand (which are sold separate from the clamps). The 30" size clamps are the most popular size since you can clamp a 24"x36" drawing from its 24" side, and/or you can clamp a 30"x42" drawing from its 30" side. Drawings that are being clamps dont have to match the clamp size, but it looks better if they do. For example, a 24" side of a drawing could clamp in a 42" clamp, but you'd have a lot of clamp that wasn't being used (a lot of overhang of extra unused clamp). Hopefully this helps you gain an understanding of how hanging clamps work!
