Jeff,
I thought the 4mm would be OK because I use it on my "Tesco" brushes.
The jets are only 4mm connectors with 1 barb clipped of I guess they are about 2mm.
Ahhh.................I wonder if it's the brush
The connector jets I make do tend to vary a bit..........I'll change the brush tomorrow
Ahhh..............................ANOTHER Brain wave
I think I'll make one of Jeff1's detachable switches for my Backpack?
David