These help reduce excessive movement of cargo in your trunk. The anchor mounts are designed for 3mm screws but I suggest testing first in a vice, etc. You may want to pre-drill a bit. I picked up a set of 1" steel rings at my local Lowes for less than $1 ea. I would not put a very heavy load on these. Use your own judgement. I printed mine out of PETG. ABS would also work. I would advise against printing these out of PLA.