The outside diameters of the ends are 4” and 2-1/2”. Just push the hoses on and clamp in place. There is one special feature of this fitting that most are unaware of. The inside diameter of the small end is 2-1/4”. The popular 2-1/4” shop vacuum hose fits in the end perfectly allowing you to connect a shop vacuum to a machine that has a 4” outlet. This usually is not the best situation because those machines come with a 4” outlet intended for a dust collector with a 4” inlet. But when all you have is a shop vacuum, you’ve got to do what you’ve go to do and this fitting will allow it.

Here’s a list of all fittings that can be easily connected:

13096 Coupler 2-1/2”
13063 Adapter 4” to 2-1/4” offset
13389 Adapter 4” x 2-1/4”
13391 Adapter 2-1/2” to 2-1/4”
13401 Adapter 2-1/4” to 1-1/2”
13402 Adapter 1-1/2” to 2-1/4”
13407 Adapter 2-1/4” to 2-1/2”
13409 Adapter 4” x 2-1/4”
13005 Dust Cap 4”
13041 Blast Gate 4” Tapered M/F
13042 Blast Gate 4” F/Threaded
13066 Blast Gate F/F 4”
13093 Splicer 4” to 4”
and 4” Hose