Sometime ago I made a small milling table fitted with a block so it can be clamped in the mill vise for those small jobs that don't justify removing the vise and re-tramming it. [I thought I had written about this tool but I guess I didn't or I can't find it. You can see it in the third picture below.] It's one of my most often used mill accessories.
The first picture shows three useful accessories made for it. (They're shown installed on the table in the third picture.] At the top is a movable-hole accessory. It's an elongated T-nut-like (see profile in second picture) strip with the hole in the center. Threaded through holes at either end of this device contain setscrews which, when tightened, bear down on the bottom of the T-slot and force the accessory up, thus locking it in place. The hole is used for a pivot pin when doing milling operations on an arc.
Below it is an arm with a rod on one end. This rod is a close fit in the reamed 1/4" hole in the middle of the table (see setup in third picture) and is used to create an angular fence at any desired orientation. Very handy for locating for repetitive operations on angled workpieces. In use, the arm is locked in place with a machinist clamp as shown.
At the bottom of the picture is a place-anywhere fence consisting of three pieces of keystock on a long, threaded rod. The leftmost piece is attached to the rod while the middle and rightmost piece have over-sized holes so they can slide freely on the rod. An extra-long aluminum handle, at bottom, when tightened forces the three pieces together and the angled sections make them displace sideways from each other. This action wedges them into the sides of the T-slots and locks them in place. Then the midmost section can be used as a part-locating fence.