Never seen them before. Went to their site and they've been dishonest right off the bat with their language.
"Proven to strengthen leaf springs..." A leaf spring is what it is. Heat treatment and material selection is what effects a leaf spring's strength.
Anything added effects its performance, not strength.
Deceptive wording is a pet peeve....
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:h 1998 GMC 2500, 10.5 Okanagan, My better/smarter half, George and Finnegan(APBT), all I need.