Yeah, ribbed plastic are factory correct. NOS replacements often differ slightly in appearance , but function the same. I used metal ones that have the factory original look and were pre-threaded.

 

Maybe these were not the right size. I had twist them pretty hard to go on and I'm not sure they went on enough. I was thinking of trying the other style with a smooth base to see how they fit.

 

There's only one size thread used from 67-81. Most likely there wasn't threads to begin with or they were screwed up. These are what I got, although I don't recall if this is the same seller. ....http://www.ebay.com/itm/1968-1981-C.../130655395797?pt=Motors_Car_Truck_Parts_Accessories&hash=item1e6bab1fd5&vxp=mtr

If you look around, you might find a better deal on shipping, geez.:sad:No problem screwing them on. Again, these are not technically correct as they're not plastic.

 

Mine looked like those and I guess they were the ones not threaded. I was nervous turning them for fear of snapping off. I ended up taking them back off and reordering. Hopefully a better fit.

 

There are some out there with no threads and you have to cut the the threads by hand as you install them. PITA because the tops can snap right off. NPD used to have a great commercial featuring these cheapo thumb locks.

 

The plastic knobs are pretty junky. We also offer the superior quality die-cast chrome knobs under part number C-10559-3 @ $11.95 (cheaper than the eBay store linked above). They're distributed by OER.

This illustrates something that commonly happens when doing your shopping on eBay. You don't have a straight-forward idea of what all is out there.

When you shop a dedicated Camaro parts website or catalog, you can quickly ascertain, side-by-side-by-side, what different levels of quality and associated prices exist. At least that's what we do. When there's a cheap-o reproduction and a better-but-much-more-expensive reproduction, we'll list them both and let the consumer choose based upon their budget, priority and standards.

Rick
NPD

 

http://shop.advanceautoparts.com/p/...orman-help-door-lock-knob-assortment-75398/9110111-P?searchTerm=door+lock+knob#

Shipping is $5 or so. This dude cleared like $1,300 selling knobs!

I gotta get into this gig...

 

http://shop.advanceautoparts.com/p/...orman-help-door-lock-knob-assortment-75398/9110111-P?searchTerm=door+lock+knob#

Shipping is $5 or so. This dude cleared like $1,300 selling knobs!

I gotta get into this gig...

Are they plastic or metal? That could be the price difference.
The ones in that link aren't even close to the original in appearance.