Small plastic insert slides into any regular RJ-14 type jack (6P4C), to change it to a handset sized jack (4P4C). A handset jack is sometimes referred to as an RJ-9 or RJ-22.
If you plug a handset cord into a regular jack without this Adapter, the plug will be loose and sloppy, causing the pins in the jack to short or move out of place.
This Insert will slide into most USOC (6 wire) Keystone Style Jacks to make them into a Handset Jack.
Also useful for adapting line cord couplers or splitters into handset cord couplers or splitters.