Profiles need an even wall thickness throughout. Large differences can cause unequal material flow through the tool which distorts the profile. Material will also cool at different rates, causing bowing of the finished extrusion.
Radii should be as large as possible. Inside radii should be a minimum of .010” and outside corners should be no less than .020” to eliminate the possibility of notching and cracking in the corners.
Plastic profiles with trict tolerances are difficult to produce because thermoplastics expand and contract at different temperatures. Greater accuracy is possible if lengths are cut off-line, but it adds cost. A typical length tolerance for extrusions would be +/- 1/16”. Longer lengths would have a greater tolerance.
Custom plastic extrusions often need to fit mating parts, such as metal frames, a board or end-caps. Whenever possible, provide these mating parts to ensure your profile fits and functions properly.