Can you post a pictue of the model.
It's really difficult to help without a picture or file.
if all you want is the def of the screw pocket, could you not simply eliminate the shaf, fix the collar t and apply the load to the screw pocket?
if you are trying to solve for the clamping force of the collar, this is a fairly simple hand calc, from that you can determine the axial loading capability based on friction.
but to answer your question...
if i am envisioning the problem correctly, you will want to place a no penetration type of contact between the OD of the shaft and the ID of the shaft collar that makes contact with the shaft.
you will need to remove all dofs such that the collar cannot slide or rotate w/o inhibiting the natural deformation of the collar. also fix the shaft.
as soon as you use non-bonded contact elements you are now in a nonlinear solver and solves time will drastically increase.