I recommend buying two 2.5 inch silicone couplers instead (that is, if you do not get the couplers with your original purchase). Hell, even if you DO get the two necessary couplers I am going to recommend getting two additional 2.5 inch silicone couplers to replace the couplers that you got. Why? Because the OEM Supra couplers were fabricated for the use of only one clamp.
For example, take a look at the first picture below. Notice that there are two indentations on the coupler. Only two clamps are supposed to be on that coupler. When double clamping, this means that there will be four clamps on each coupler (aka two on one end of the coupler and two on the other end).
Before I forget, I strongly recommend you double-clamp practically everything associated with this install. Personally, I wouldn't care if I had all the T-clamps I could possibly need. I would double-clamp everything. Therefore, since the OEM Supra couplers were fabricated as such, it is not very comforting that one of the two clamps will not have the best "hold" as it should have.
Here are some photos of the two MKIV Supra couplers that I utilized. The first four photos are of the coupler that attaches the exhaust adapter to the bottom end tank. The other photos are of the coupler that attaches the other exhaust adapter to the top end tank.
The photo below shows the outside diameter of the Supra coupler (if you have bad eye sight, the OD is 3 inches)
The photo below shows the inside diameter of the Supra coupler (if you have bad eye sight, the ID is 2.5 inches)
This coupler is the one that fits through the infamous hole (the hole that nearly everyone says must be cut).
