I also gave thought to a sleeve mount, but nixed the idea for a number of reasons:
1. I wanted my mount to be flush with the floor so that it would not be a trip hazard when not in use. A sleeve mount left flush would not allow the use of a pin to lock the tool to the mount.
2. I needed the mount to be capable of being used in a very solid and rigid manner. A sleeve mount would not provide this, as woochucker mentioned. Too much freedom of movement.
3. I wanted the mount to be quick and easy to use. Threading in four bolts, then snugging them up with a wrench takes longer than a sleeve mount, but it still does not take much time.
Problems with my mount:
1. The coupling nuts can fill up with dirt. This is easily remedied with compressed air.
2. The threads in the nuts might rust and get tight over time. It is easy to run a tap through them.
3. The coupling nuts need to have the bottoms capped in some way so that concrete does not flow up through them when you pour. Easily done when fabbing them up.
4. A person must be careful to not strip the threads out of one of the coupling nuts. Since they are 1/2" in size, I don't think this will happen very easily. The bolts never need to be tight anyway, good and snug is all that is required.
It is not perfect, but so far it works quite well and meets all of my requirements. I also have a single leg vise that I can mount there. It is really nice being able to work all the way around a vise on some projects. I've been thinking about making a small (24"x24") welding table that will mount there also. With just one central leg, there would be little to get in the way of odd shaped projects. The only drawback is that I have found that it would be nice to be able to mount more than one tool at a time, so plans are to make and install three more mounts this coming summer. If I only put in one or two, you know darn well that I will eventually need four!