This is a clip designed for the AK-I and AK -II and AK Duos (regular, medium, and high pile) to allow you to use a spring balancer with your machine that takes the weight off of your arms. 

What is a spring balancer:

A Spring Blancer that can be mounted to your ceiling to keep your machine suspended and reduce fatigue on your body and hands. The Balancer can also be mounted to your tufting frame however this model is slightly shorter.

It also helps to prevent damage to your tools by having them suspended as opposed to being set on a table.