Dorian TIN354-32 screw size

[Froneck]

I posted this question in Antique Machinery forum and got a suggestion to ask it here. I have a Dorian TIN354-32 mounted on a Dorian CXA quick change holder. Looks new, no scratches or any sign of use. Perfect condition. Dorian site listed GTS-1 as screw size. Order a pack of 10 that are 3.5mm-.6mm but are too big. Having #3-48 and 3-56 taps near I tried them but Taper tap would screw in a few turns the stop, OK wrong pitch. I purchased a 3mm-.5mm tap same result but it added a tap to my collection I didn't have. Checked tap drill size wit pin gauge, .091" fits well, .092 will only go in about 1 thread. 4-40? so I tried 4-40 tap then a new hex head cap screw., same thing taper tap screws in a few turns then gets tight, screw will go in maybe 1 turn. Can't be 4-48 because 3-48 would have easily went in.
Anyone have any idea what the screw size is? Only size in McMaster is 3mm x .5mm