Some of them make the lock stitch, others the double loop stitch, and still others the single chain stitch.
The reply to such a query is, of course, that to produce the lock stitch in that way is impossible—as indeed it is.
The shuttle is perhaps the most important part of a lock stitch machine.
The two chief types of machines are the lock stitch, using double thread, and the chain or loop stitch, using a single thread.
Has the under-feed, makes the "lock stitch" alike on both sides, and is fully licensed.