what size is the star bolt on a seat belt on the 84 t-bird?

Answer 1

#50 Torx

Answer 2

it's called a Torx head and it's probably in the area of a T-45. Torx bolts come in a variety of sizes from as small as T-4 or T-6 all the way up to the biggest I have ever used, a T-60 which is used on the front caliper mounting bracket on GM W-cars up to 95 or 96. They also make Torx bits in tamper resistant in which they have a hole in the end of the bit that corresponds to a small pin in the center of the star on the bolt head. Try not to use a tamper resistant Torx driver on a standard Torx bolt because the tamper resistant torx bits are weaker due to the hole in the end.