Constructing Stands for Quads

Hello All! I am having a local welding shop make up some stands for my Quad 988's. I'm thinking of lifting them 12-14 inches off the floor (any comments on height?). They will be made of 1/8" wall 1.5-inch square steel tubing, primed and painted. I'm not sure if they will be able to accomodate lead shot. They will connect to the floor using three points (tripod effect), and I would like to be able to switch between spikes and locking coasters at my discretion. Any suggestions for where to get either of the two, hopefully both threaded the same, for not a ton of money? Thanks.
Whoops, did I say "coasters"? I meant "castors".
Beware of the potential for mid/upper bass suck out if you elevate your speakers this high. When I set up my 63's I ultimately put them on the floor - I had acrici stands but retired them. W/O the stands they had a near flat frequency response in my room down to 35hz. W/the stsands the sound thinned out substantially. Experiment before you commit.
Thanks Newbee. Good advise. I will experiment using cinder blocks first. The room I'm currently in (part of a rental house) has somewhat bloated bass response with the Quads on the floor. However, I plan on moving into another house in the next six months, so that could all change. BTW, I've priced out custom construction of the stands. It sits at around $600 for 12-14" high stands. One Agon member (kjl) had 28" stands made custom, and really liked the result.