Singer made the early 66 class machine with a back-clamping foot arrangement (as opposed to the side-clamping arrangement common elsewhere) that was not used on their other machines. Although it was superceded fairly quickly, the enormous quantity of these machines that were made, and the hard-wearing nature of all the early machines, mean that there are still many in circulation. So these are useful still.
I don't get many back-clamping attachments, and some types of feet have never been available for these machines. If you want to do quilting or machine embroidery on a vintage machine, I recommend you look for a 15 class machine....
You will know if you have a Back Clamp machine if its ordinary foot looks like this:-
BC012 Regular Foot; £5 with attaching part; BC012a; £4.50 without, all with screw(s)
BC006 Back Clamp Ruffler Foot; £8
BC008 Older-style Back Clamp Ruffler Foot; £8
BC004 Back Clamp Narrow Hemmer; £2-50
BC003 Back Clamp Adjustable Hemmer Foot £5-00
BC009 Back Clamp Binder Foot; £4-50
BC005 Back Clamp Quilt Foot £7-00
BC001 Back Clamp Tuck Marker; £8
BC002 Oldest style Tuck Marker; £10
FS072A Back-clamp set with good green card box, comprising seam guide and screw, binder, shirring plate, underbraider, ruffler, quilt foot, bias guage, adjustable hemmer, tuckmarker, and narrow hemmer; £45
FS074 Similar to FS072A, plus feed cover plate, screwdrivers and stiletto, three bobbins, and needles; £50 (I may be able to find a box for this)
My address is:- 4, The Raveningham Centre, Beccles Road, Raveningham, Norfolk, NR14 6NU. United Kingdom 01508 548137 email@example.com