Here is my spider-rigging rod holders and base. I used 1/2 galv. pipe for the upright. I then used 2-12" of 3/4 galv. pipe and 3/4 T for my T-bar. I used a 3/4 X 1/2 reducing bushing to attach upright to T-bar. I used 4 split-ring pipe hangers for 3/4 pipe for the bases of the driftmasters. You can loosen 1 of the bolts that hold them together to adjust the height of your rod tips.
For the base I used a 1" floor flange mounted to the floor of my boat and a 1" X 6" pipe nipple. I then used the nut and washer from a 1/2 dresser coupling to mount the 1/2'" upright to the base. I drilled a 1/4" hole thru both and used a pin so the upright could not twist. The dresser coupling nut and washer take out the wobble. Just pull pin loosen nut and the rod holder can be removed.
Here is the split-ring pipe hanger that I used.