Almost all, but not all, Featherweight cases have keyed locking latches. The later Featherweight tan and the white Featherweights did not have locking latches - with good reason as explained later in the blog.
All black USA 221 Featherweight cases had "flat" keys.
All 222K carrying cases are black with keyed locking latches. Most of these cases were made in the UK and had the "3 dimensional" key that was also used on UK manufactured 221 Featherweights.
A few 222K carrying cases use the "flat" key. These cases were made in Canada and have "Made In Canada" imprinted on the underside of the carrying case.
Over the many years we have been acquiring Featherweight sewing machines far too many cases have had either latches forced open or hinges broken because cases have been locked and keys lost.
Locking the case serves no purpose. If someone wants to steal your treasured Featherweight they are most likely going to grab the case handle and walk off with case and machine.
Singer finally caught on about how keys for carrying cases were not needed. The Canadian tan 221 Featherweight and the British white 221 Featherweight cases, both of which were produced in the early sixties, had non locking latches.
Unless you need a key to complete "the set" don't worry about getting a key. If you feel the need to have a key (and yes we sell them) don't risk locking the locks. Attach the key to the case handle with a decorative tie and leave the case unlocked.