...the working opening is only about 1/2 with the red disk, which can come loose since it is only threaded on. To get 1 one must use without the disk. Interestingly, this is almost identical to the Zona SMALL C-CLAMP 5/8' ZON37215 and found that the parts are interchangeable. Both have threads cut for the bolt, but the Mascot feels more like a friction fit. Something to consider is that this weighs 1 oz., and be sure to compare the pricing.