I have made a number of those out of the SS hose clamps myself of identical design.
One word of caution to anyone making one, especially with a hand drill and anything other than a fresh drill bit, CLAMP that little bugger down. Because of the weird way SS is both hard & soft-ish at the same time, and because that material is so super thin, you'll have a tendency to really bear down on the drill to get it going and before you know it, it will be about 2/3 of the way through and catch and want to spin that little SOB and take your fingers with it. A drill press & a sharp bit will help, but even then, the clamp is the most important part. I like the Idea of using AL and the added advantage of it being a little thicker so that the hole can get going a bit before it starts to break through. Still, clamp for the good of the fingers. I suppose punching the holes would be by far the best, but that exceeds my garage fabrication abilities.
As the physical, emotional, and spiritual scars have all finally healed, I may try the AL next time I need a couple, or take the time to set up properly rather than rush the job in between items on the wife's to-do list...
or even better, just add them to my next order from Bryan...
Happy rod holder-ing,
Fred