I bought a pair of those for my -9A. They weren't expensive and my rational was bracing to support the horizontal stab and prevent failure. Seemed logical to me and my A&P shrugged and agreed. I didn't install them after reading what I remember to be a rather scathing indictment of those braces in a thread here on VAF. IIRC, the gist was related to installing "gonzo engineering" without "appropriate stress analysis" and engineering endorsement from Van's. The thread is somewhere in these forums. I took those opinions with a grain of salt, but never did install them. I'm sure they're sitting around in my hangar somewhere. I might go ahead and put them on someday after I pull the fairing for a CI. Or not.
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