Singer Featherweight Slack Thread Regulator & Screw, Tension Unit, (Vintage Original)

This tension unit piece (part 45863) regulates the slack produce by the take-up spring. The little screw that holds it on is also included (part 335), which may be chrome or black, depending on stock availability at the time the order is filled.

This part fits the Singer 221, 221K, 221J, and 222 as well as the Singer 301.