The pipe sizes for the SpeedRail fittings are:
Most chainlink toprail is either 1" or 1-1/4" IPS size. So re-measure your pipe before setting up an order.
The #5E Tee-E fitting has two
set screws that face the same direction, one for each piece of pipe. Just fine for crossbars—what I buy, mostly.
The #5 Tee has three setscrews, with one at 90° to the other two. Better for joints that might get rotational stress, e.g. a drop footbar. Not good for oarstands, since the double setscrews face into the boat tube.
For oarstand mounts I'd use the #15 Nu-Rail Offset Tee (only in 1-1/4" IPS) or a #10 Offset Cross.
You can download the catalog at http://www.hollaender.com
and figure out what exactly you need. Let me know with a PM and I'll check prices.