They come in a variety of styles and quality,but most of the ones I go for now are made by Ariel,Parisian Novelty,Novelty Cutlery,PAL,and Remington.Most were used as advertising gimmicks and given to valued customers.
Here are some examples:
First is a Parisian Novelty Co. These were mostly metal handled but I have a couple that have a plastic like overlay on them that contains the advertising.A lot had a replica of the customer's signature on one side.Nice for counterfeiters to copy.
Next is an Aerial Cutlery Co. with pearl celluloid handles and a Masonic emblem attached.From what I understand,when Aerial knives were a hot collectible,people would get these and cut off the letter opener blade and pass them off as regular pocket knives.Same with Remingtons.
Next is an Ambassador.This one is slightly smaller than the first two and uses an inlaid celluloid scale on a brass liner.Ambassador made pocket knives as well;most notably the little 2 blade circular ones.
Next is another Ariel advertising Andis Clipper Co.;makers of nail and hair clippers dated Christmas 1965.Must have been an employee gift.They are still in business today.
Next one is a bit unusual.The handle is a piece of extruded aluminum channel and the blade slides within it.There is a set screw on the back(use a coin to loosen and tighten)to allow either the letter opener blade or the other end which is a box cutter type blade to be exposed.
Next is a REALLY unusual one:A letter opener that has a so-called,"funny folder"knife on one end.First one I've ever seen.Not sure what the notch on the handle is for.
Next is a brass handled one with a fancy Celtic design on one side.Don't remember if this one is a Remington or not,but Remington made this style.Blade has a ruler engraved into it.
Last one for now is a letter opener/scissors combination that operates like a Barry Wood folder:Lift the handle and rotate the assembly around and a pin engages at 180 degrees and opens the blade.Continue around the full 360 degrees and the handle pin drops back into the frame and the blade is fully open.Both blade and scissors operate the same.
All for now.I'll have some more to put up later.