5-gal. Plastic Paint Mixer with 15 in. Round Metal Shaft

The length, width, and depth, of the blue paddles are each 3-1/2", so, unless your bucket's openning is wider than that, it will not fit. Most screw-on holes in such buckets or cans are at the end, rather than the middle of the can, so, removing the top, completely, and threading the "naked" end of the mixer bit through it won't work as well. Suggestion: Take an old lid or something else that is solid, heavy, sturdy, and wide enough, to fit over the entire bucket, and drill a 3/8" or slightly wider hole through the center of it, then push the "naked" end of the mixer through it, then, attach the drill to it (i.e., chuck it on), then put that lid over the bucket, making sure it is secure (use bricks or a helper; also, make sure there is a tarpaulin or similar under the paint can, and that the rest of the work area is similarly protected). Turn on the drill SLOWLY, at first, then, gradually, run it faster, making sure at ALL times that the lid is secure and that you have control over the mixer and drill. If you think you're going to use the entire bucket's worth of paint/stain, then drill through that lid; since the drilled hole is only 3/8" wide, it should be easy enough to plug with duct or other heavy tape (naturally, you should use as much of it as you can, as quickly as you can, lest it solidify with contact with the air, no matter how well you seal it). See the attached image showing a cutaway view of the paint can with the mixer bit going through the center of an orange "lid."

The length, width, and depth, of the blue paddles are each 3-1/2", so, unless your bucket's openning is wider than that, it will not fit. Most screw-on holes in such buckets or cans are at the end, rather than the middle of the can, so, removing the top, completely, and threading the "naked" end of the mixer bit through it won't work as well. Suggestion: Take an old lid or something else that is solid, heavy, sturdy, and wide enough, to fit over the entire bucket, and drill a 3/8" or slightly wider hole through the center of it, then push the "naked" end of the mixer through it, then, attach the drill to it (i.e., chuck it on), then put that lid over the bucket, making sure it is secure (use bricks or a helper; also, make sure there is a tarpaulin or similar under the paint can, and that the rest of the work area is similarly protected). Turn on the drill slowly, at first, then, gradually, run it faster, making sure that the lid is secure and that you have control over the mixer and drill. If you think you're going to use the entire bucket's worth of paint/stain, then drill through that lid; since the drilled hole is only 3/8" wide, it should be easy enough to plug with duct or other heavy tape (naturally, you should use as much of it as you can, as quickly as you can, lest it solidify with contact with the air, no matter how well you seal it). See the attached image showing a cutaway view of the paint can with the mixer bit going through the center of an orange "lid."