Talked to Tilton. Here's what I got:
Their aluminum and magnesium bells are not SFI rated because their applications do not require the certs.
They do not make steel anymore and only did because IMCA required it for awhile.
He has never in his 15 years seen or heard of any of the Tilton clutches exploding and going thru a bell.
The magnesium and aluminum bells would not sustain a hit of an exploding it was to happen, but these types of racing clutches are not the type that explode.
Their clutches are tested up to 26,000 rpm.
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Ok I feel better but not sure how much better...
Jerry, maybe that's why your picture is about 30 years old and black and white because these don't really explode anymore like he mentioned?