I think I got sent the arms for 81-87, there's a shape about the skirt around where the post goes in that hits the bolt that holds the post assembly onto the cowl. When fully engaged, the arm sits about 3" up off the glass.
[Insert bleepable string of words and select phrases here].
So I figured screw it, just put on a set of bayonet base blades. From Napa. $31 that won't go for fuel. Sheesh.
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Notice the shape of the area where it goes on the wiper arm post.
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The finger closest to the post mount shows where, in the design of the arm, the skirt of the housing swoops low to accommodate how they set the tension spring mount. That feature hits the screw being pointed towards with the transistor radio whip.
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It's literally been 2 years since I got these and don't remember from where.
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Still can't decide if the SILV means Silverado or silver, the color. Either way, a swing and a miss. Maybe later I can upgrade to modern blades too.