Inaccurate nut sizes in prints

I'm using a MendelMax 1.5 with Slic3r, and printing with PLA at the moment, and I'm able to get decent prints, and everything is very accurate. A 10x10mm box comes out as 10x10mm, etc. The ONLY thing that prints way off are hexagons (6 sided polygon). eg. When I embed a RECESSED 9.5 mm x 8.5 mm hexagon into a surface (as opposed to printing a solid hexagon), it prints as 7.9 mm x 7.3 mm, so nuts don't even come close to fitting into the hole. That is way off. Everything else in the print is bang on. Is there a reason for this? Has anyone else experienced this? I know that obviously I can increase the size of the hexagon, but I want it to print the same on all printers.

EDIT: Nevermind, I think I got it. Tried to delete my post but apparently there's no option to do so.

Edited 3 time(s). Last edit at 02/20/2014 01:10PM by mza1979m.

Tell us what did you got ... maybe and other people have the same problem..

Good idea...
I guess when making a recess in the shape of a polygon in a surface, first instinct would be to take a calliper, measure the nut (from flat side to flat side, and from corner to corner), and input the measurements into the software. But that doesn't seem to work, and it's hard to explain why. So I simply measured one of the SIDES of the polygon and ensured I matched that up with the sides of the 3D model. I had to print a few test prints to get a perfect fit, but unless I did it this way, I'd get a hole that was way too small for the nut.