in the second picture, the rod on the bottom left would go through a bracket mounted on the top of the bass drum. the rubber end would rest on the bass drum but I have seen pictures where it is not. Google it....you can find pics of it in use.
You use it to turn a floor tom into a bass drum and mount a tom on the drum using one of the brackets for the floor tom legs. You put the floor tom on its side, slide that rod on the bottom left in the second photo into a leg bracket and now you've got a rail mount you can use to hold a tom. There is also a Dunnett companion piece ... gull wing spurs that go in the other two leg brackets of the floor tom to complete the conversion from floor tom to bass drum.