sweep sets or "engineers curves"

  "Half to forty"

Engineers curves, body profile gauges, or "sweeps"
These are rare to find, using the original chart, these are laid out on CAD, then accurately laser cut from the binary, from 4mm alloy. Each has its individual number etched onto the side, they are numbered; half to number 40, they are supplied with or without the stand that has five castors on the base to aid movement in the workshop. Alternatively they have also been cut with holes for wall mounting if you prefer. They are 4ft in length, and I can produce half scale versions too, if you desire.

what are they?

A measuring tool. It aids the panel maker to produce identical panels, say each side of the vehicle or aircraft, you would pick the profile to match the profile and then reproduce the corrosponding panel to that particular number, most professional sheet metal workers will have a set, they are a standard formula, so in fact panel makers at each side of the world could produce identical work in theory!