If you don't want to buy this spare part for $20, you will like my self designed model!
Step 1: Print It.
Print it with ABS and 100% infill. I never tried it with PLA and I don't think it would work.
Step 2: Insert the Nut
You will need one M4 nut. Just insert it like in the picture above. If you don't want it to fall out, you should use some superglue to hold it in place.
Step 3: Use It!
You are done!