I think you and the other guys are talking about two different kinds of taps. They are assuming you are tapping copper to thread machine screws into, and you are trying to tap the plexi top to thread a hose barb into.
6-32 is a machine screw size. The 6 specifies that it is a number six diameter thread, and the 32 is the number of threads per inch. Straight thread sizes below 1/4" are referenced by numbered sizes for simplicity (or complexity, depending on how you look at it)
When getting a straight tap to tap a hole for a 6-32 machine screw, you need to make sure you get a #6 diameter tap with 32 threads per inch, or else the machine screw won't fit in the hole when you're done. If you find any old #6 tap, it could be a coarse thread or fine thread tap (signified by NC or NF). The standard NF thread count for #6 hardware is 40 threads per inch.
There are different kinds of pipe taps, but you shouldn't ever have to use anything but NPT (national pipe taper). The NPT standard lays out exact thread shape, the angle of taper, and the number of threads per inch for each size. If you have a 1/4" NPT threaded hose barb, and a 1/4" NPT tap, you do not need to worry about any other factors. They are completely compatable per the standard.
1/4" NPT tapered pipe tap
three types of straight-thread taps (the difference is the amount of bevel on the leading edge)
See the attached tables for more insight on standard sizes and their respective thread counts for both straight thread and NPT thread. Lemme know if you want any more info, and good luck with the block!