This is a nice original low shank straight stitch foot and thumb screw. It is part # 45321 and will fit Singer models 15, 27, 28, 66, 99, 101, 185, 192, 201, 206, 221, 222, 306, and 319. This product is available from Central Michigan Sewing Supplies.
5 Pcs Thumb Screw for Singer Vintage Sewing Machine Feet Attachment Presser Foot
Singer LOW BAR Shank Screw-On STRAIGHT STITCH Presser Foot
Straight Stitch Foot By Singer for Low Shank/Vertical Needle
Sewing Machine Feet Guide
presser foot - The Singer Featherweight Shop
Vintage Original Singer Low Shank Feet & Attachments – Central Michigan Sewing Supplies Inc.
Introducing the Original Singer Sewing Machine Low Shank Sew-On Button Foot - Part # 161613. This innovative foot is designed to securely hold any
Original Singer Low Shank Sew-On Button Foot - Part # 161613
presser foot - The Singer Featherweight Shop
Singer Model 221 Sewing Machine Parts: Original and Replacement – Page 10 – Central Michigan Sewing Supplies Inc.