Restricting rotational movement

I’m looking for an elegant mechanism for restricting the movement of the wheel cradle in the picture.

The wheels are intended to be able to swivel around +-5° but not more.

The initial idea is to have some kind of pin and a slot in the front plane. Is there an established way of making the axis itself somehow reduce the swivel?

• The axis needs to be round in shape (no hump); there’ll be tightening clips around it
• The forces to the rotational direction are minimal, i.e. just gravity