Thanks for the reply.
I don't think there is any out there like you discribe, nor would I want them.
First I think tolerance stack up and differences in manufactures ratchet design would make it difficult to ensure positive lock up. Ie if ratchet manufacture A ball detent to end of anvil was .050" to short and manufacture B ratchet .050" to long. Ratchet A might not "lock the extension and ratchet B might not even engage it's ball detent.
The length differences should not be an issue. Just have the locking start early enough that any reasonable ratchet design would be long enough.
Problem 2 would be ball detent strength. Ratchet with push to lock features might not have an issue but ratchets with straight ball detent a might get pushed off by the locking rods spring. What about impacts with hog rings?
I agree that a spring-loaded ball may not work well, but with a push to lock ratchet, that is not an issue.
Problem 3. It would weaken the shank being hollow.
There would not be much of a loss in strength since the center does not add much twisting strength. That is why a driveshaft is hollow. Also the outer diameter could be slightly increased to compensate.
Problem 4, I use a snap on 12" 3/8 locking extension constantly. I am an industrial mech (but also used this method as a heavy/farm equipment mech) and start fasteners with the extension itself and only use the ratchet to to finsh tightening. Many times you can't get your hand into a place so you place a bolt or nut into the socket(or in industrial work a cap screw on a hex socket) and stick it in the hole and start the bolt. You can feel thread engagement and not cross thread like you can using a ratchet or impact to start fasteners. After all fasteners are started then I hook up the ratchet or m18 impact and run everything down. The type of extension you propose it would be impossible to do that.
I know what you mean about using the socket+extension to fit where your hand does not. With an internal lock, you would have to put the ratchet on the extension+socket+fastener to lock the socket then remove the ratchet and start threading by hand (when the socket could slip off if you pick up on it). That is more work and there is a chance you could forget and lose the socket. But it would be convenient to have the socket lock and unlock automatically. Not sure if that would outweigh other disadvantages without trying one for a while, although if nobody makes one that probably says something.
