Spool Holder for 8mm Threaded Rod

Having tried a couple of spool holder designs I found they didn't seem very strong - they didn't use much material and I could snap them in half with my bare hands. Not liking the idea of it breaking in the middle of the night I set about designing my own. I wanted to see what the Design Spark Mechanical freeware was like so I used that. The 125 Meter cardboard spools from Diamond Age which is about 100mm radius set the spool size to accommodate, but here is room for 125mm. I printed in PLA and could have used less material but I wasn't to bothered about saving a few grams of PLA so left as is. I use http://www.thingiverse.com/thing:5634 to hold the spool.