The clips on my bookshelf kept breaking when my cat would jump on the shelves, as a result, I designed these using fusion 360 and they work great! They are a very easy print that most printers can do very easily. I tested them on my CR-10 and Monoprice and both worked great. Printed in PLA the hold a surprising amount of weight and have a snug fit into the holes. if they are too big just shave a little plastic off and you'll be set to go. 

I used:

100% infill

2 perimeters

no support 

60mm/s

total print time 10-15 min

Happy Printing!!

-Monarch