When troubleshooting telephone wiring, sometimes you need to work with individual leads. Also, the typical “butt set” tester includes alligator clips rather than a modular plug. In both cases, the tool you need to make the connection between the leads and the modular plug is called a banjo.
Banjos, also called “modular test adapters” by suit-wearing folk, are available from a number of makers with 4, 6, or 8 wires. Most have a clip on the back so they can attach to your bat-belt, and some include handy features like wiring charts printed on the face.
Ideal builds polarity test lights into their “Smart6” adapter, and Progressive (now owned by Greenlee) builds a whole toner into their “AdapToner” series.
Street pricing starts around $20 for the basic models.