Four features is the correct way to make the model, but that's too many features for a low feature count challenge.
Two features was my lowest:

I didn't work out the proper dimension for the slot when making the above model. It's a silly way to measure a slot, and dimensions are not usually the challenge in these posts.
But, in the spirit of Bob's post, I did some trigonometry to determine the depth of the slot needed to obtain the correct angular slot depth.