In the film industry, ordinary wooden clothespins are used to attach colored plastic gels to lights and they’re called C-47s.

A prominent visual effects artist told me an origin story of the phrase:

Back in the early days of Hollywood, studio heads would do audits and they’d see that the lighting departments were spending a ton of money on clothespins. And they said “we’re spending all this money on clothespins. This is ridiculous!” And they shut it down you know,  not understanding that the clothespin is a very important tool for lighting that we use everyday. So the lighting guys started calling them ‘C-47s’ so that when the big-wigs saw so-and-so hundred dollars for C-47s and they said, “Oh sure, ‘C-47’ that sounds important, no problem.”

As a film student, I’ve heard several contradictory stories about the phrase C-47. Some of the other prominent origin tales are that they were names after a WWII fighter plane by returning soldiers turned filmmakers, or that C-47 is the patent number.

All of these stories are equally unverified. In practice, the lingo ‘C-47’ mainly serves as a test of membership on film sets. If you’re a newcomer on a set and a grip asks you to fetch a C-47, you have no idea what they mean and are forced to ask someone. It’s embarrassing to realize that a C-47 is just a simple clothes pin. The lingo functions as an inside joke, and an initiation that everyone on a film set must undergo.