I don't know exactly what you are looking for but our "hard couplings" for aspiration in the shop use either:
- PVC 40mm (x2mm) plastic piping, standard code european drain pipe (40x3.5) will NOT work , use the "low grade" stuff sold in many DIY outlets
= 40mm (x1) copper piping with large arc bends (or better yet sandfill bends) assembled with tin solder to keep it as hard as possible (I haven't tried epoxy glue, but it should work)
One great thing is copper to plastic dilatation joint couplings, with an O-ring inset, they will slide perfectly onto the tool output manifold, just the right tightness and easy to mount/dismount (no degradation, no screws, no falling off) a slight film of dry lube on the o-ring from time to time is perfection
Care must be taken to de-barb the cuts in the rigid pipes, the smooth interiors are more prone to jamming than corrugated hose
good luck
