T-bolt clamps have overlap as they go up in size. When I started making MAF pipe and up-pipe kits, it became a NIGHTMARE trying to find the ''perfect sizes'' that would work in all cases. (and making them the same style, color, and brand)
What you're running into most likely has to do with stuff not being exactly 3" and 2.5"s. For example, an LT1 MAF is bigger than a normal 3" stock MAF. So is a stock turbo bell .vs a intergal bell turbo. The throttlebody is larger than 2.5" too. They all require oddball stuff.
Another thing that might be tripping you up is silicone coupler thickness. A thicker than normal coupler can knock a T-bolt clamp out of range. They aren't like worm screw clamps, where you can change the OD several inches.
If the ones you're looking at have something like ''3"" or "2.5"" stamped on them, the manufacturer has accounted for coupler thickness (and sometimes guesses it right). A 3" clamp, for instance, will be sized for a coupler that fits over a 3" pipe. The problem arises when you either have thicker than normal couplers, and/or if the coupler is swedged out a little from being stretched over a LT1 sensor, stock turbo bell, or throttlebody.
I would recommend avoiding the ones with the springs. They may look ''trick'' but why in the world would you want an important clamp to have a 'relief valve' so you can send the up pipe into the hood?