Ok, I checked it out at work today, and I will admit I was wrong about one thing. It seems as though the cutoff year between t50 and t55 was 93. 93 being the first year of the t55, with everything before being t50. This is on Rangers only. With the f150 up to f350, it is still a t50. Strange that they would do this, but it's true. The difference between a t50 and t55 is unmistakable, a t50 will fit into a t55 bolt, but will just ever so barely grab the edges, the first time you turn it, it will either take out the bolt or the bit. The t55 won't fit into a t50 bolt, no matter how big of a hammer you try to persuade it with.
This is a picture of a t50 in a 99 f350 bedbolt, ordered new from ford. These same bolts I used to replace the ones I cut on my dads 88 Ranger.
This is an 06 f150. T50
I also tested an 01 Ranger, but didn't get a pic cause my camera was full. It was indeed a t55.
If anyone can find a ranger between the 93 model year, and current, that is t50, please take a pic with bit in it, and post it up, I will do the same. I am curious to see if they changed back to t50 after 93.