T1 is the 'pagkage' specification. In electrical components, there are hundreds of differetn devices that use the same 'package' for uniformity. The filters ('bulb condoms') are designated by the size of the bulb they cover, (at least on mouser.com) and so that's how I refer to them. The Automotive industry likes to have differetn designations for everything, but the electrical component industry is where all this stuff comes from in the first place.
Ignore T3 It's not used anywhere in the dash, radio, hvac, key ring, or door controls. T3 = #194, T3-1/4 = #68, T1 = #74, T1-3/4 = ? (haven't found a direct replacement in the automotive world yet)