Concerning "classic" hoses and LDCad

[Philippe Hurbain]

has outer and inner radii of 5 and 3, respectively—but I couldn't figure out how to get a ring primitive with those radii. Surely there must be a way?

The simple solution is to use a ring3 and a ring4 (scaled 1x). For more complex cases there is the ring and cones calculator, in tools section of LDPE (see also http://www.philohome.com/isecalc/rings.htm for a stand alone version) . Technically (less vertices) it would be better to use chrd+ndis primitives+quads but it's more complex and not worth the trouble here.