The Vixen 4" f/9.8 I bought did not come with the top strap between the rings so I cut one out of 1/4" thick by 1" wide aluminum bar stock. First one I cut and drilled has one hole slightly off center (about 1/32" off center line). Works fine but I cut another one, so this one is available. You supply the 1/4-20 x 3/8" or 1/4" thread length socket head cap screws. (See photo)
I believe a rigid bar is better than a strap because it makes holding and mounting the telescope easier and it give you a platform for either guidescope rings or a piggyback bracket. See photo of bar. $10 includes postage if anyone is interested. U.S. sale only, personal check or money order please.