You may be wondering, what the heck is a short flange adapter and what good is it for. A normal M42 to E-Mount adapter would allow the mounted M42 lens to focus to infinity; a short flange M42 to E-Mount adapter is made as thin as possible with only one purpose: to be used with another adapter, usually a focusing helicoid that has an M42 mount. Definitely not usual and is a bit hard to find. I was very happy to have found one.
Yeenon adapters are usually more expensive than other makes from China, because their stuff is better made with good precision and this particular one came with a nice box, and a rear cap. The adapter cost $15 plus $8 shipping.
Before buying this adapter, I was using a modified C-Mount to E-Mount adapter that has an inner 42mm thread, but this kind of adapters are now hard to find. Most C-Mount adapters sold now do not have inner threads.
This adapter fits the Yeenon helicoid like a glove. It also is very precisely made and mates to the Sony A7 with a snuggle fit and no play at all. The fit and finish is first rate. Very happy with it.