Depends on where they're loose. The "feet" on the lock down handles are threaded so you can raise or lower them as needed. Two things to consider here. There are supposed to be little rubber bumpers at the tips of the threaded feet. Those little rubber bumpers are often missing. This would could the top to fit a little loose and also scratch up the interior plastic trim since the rubber bumper also serves to protect that. Also, you don't want to adjust the tops too tightly because you take a chance on cracking the t-top glass. I know somone that just installed new t-top weatherstripping on a vette. The new weatherstripping was thicker than the old and he didn't take that into consideration when he put the tops back on. Cracked both tops.
The other way tops can fit loose is that the slots on the t-top frame that you slide over the tabs on the roof can get wallered out causing them to not fit tightly. They make a kit that you clip onto the t-top to "fix" this problem. They are basically U shaped clips with the correct size slot cut in them. You snap them on over your worn out slots.