Beginner question about constraints

[SUPFRESH]

Hi, the part im modelling is essentially a triangle with a hole at each corner. all nodes at all holes are constrained to only move in the xy plane. also,one hole is a pivot (but for the purpose of this analysis can be considered constrained), one is fixed in all directions and rotations and the other is unconstrained (except for the xy plane condition mentioned earlier). I have a gradient pressure force exerted on half of the inside of the unconstrained hole. My problem is at the moment the pressure obviously deforms the unconstrained hole. However, the force is exerted by a metal rod/axle inside the hole. How do i constrain deformation of the hole. Or to ask it differently, how to i constrain relative movement of the nodes surrounding the hole, with respect to each other? I'm using solid185 if that makes a difference.

thanks in advance