ChiaoGoo Cable Connectors
These small double-ended screws allow you to connect two cables to make a long one. I use these constantly for trying on in-the-round sweaters. When I'm ready to have a try-on, I unscrew one needle, screw this in and add a longer cable, and pop it over my shoulders to check out the fit.
The screw join on Chiaogoo cable connectors come in 3 sizes, Mini, Small and Large. Be sure to select the size that matches your cables.