Rear disc brakes

I have a 97 w/4 whl disc brakes. I know you must screw in the rear caliper piston to compress it when replacing pads. I have the tool for the job but it seems that there is a point at which it will not screw in further. I was afraid that the piston was stripped so I removed it from the caliper. The "thread" is very coarse, almost like a groove so stripping would be very unlikely. My question is do you screw it in as far as it will go then compress it with a clamp? I did complete the job but this is nagging me. Any thoughts?

I have done the rear brakes on my 97 Sable 3 times, and 2 times I compressed the caliper piston with a set of needle nose pliers, with no problems. The 3rd time I finally bought the proper tool, and found it more difficult, like you mentioned. All I did when it got tough, was to reverse the direction, and back it out a bit, then tried again. I am not sure, but the threads may have had some gunk on them. Since you have it apart, why not try some brake piston grease.
Also, remove the pins and boots (mounting) and make sure they are clean and grease with the same caliper grease. I have had problems with those pins rusting up and locking up the caliper, thus burning out the brakes.

Thanks, TJ. I usually use anti-seize on all mounting hardware. I know I'll be back in there sooner or later and don't want to have to fight it too much.