Top Hat or High Hat screws on FI

[Harry S.]

Re: Top Hat or High Hat screws on FI

What is the overall length of the FI screw?

[Keith B.]

Re: Top Hat or High Hat screws on FI

66 Chevelles used the same screws as well in the interior

[John H.]

Re: Top Hat or High Hat screws on FI

We mis-used those "top hat" screws constantly at Willow Run on the '65-'69 Corvair lower tunnel cover and on the steel retainers for the rubber engine-to-body seals, instead of the specified ordinary 5/16" hex sheet metal screws; the tunnel cover used about 12 per car, and the engine seal retainers used about 18 per car. We beat up Engineering constantly to release them, and Finance refused, as the top-hat screws cost about four times the piece cost of the regular (released) screws. We just kept mis-using them and let Material Control worry about it.


HighHat2-1.jpg

[Michael G.]

Re: Top Hat or High Hat screws on FI

John, that scenario was pretty common back then, for many, many fasteners. I remember one bolt that the line operators really liked. The supplier had permission to build only 5 million a year, but so many operators had switched to it on their own that the plants were ordering 5 million per month.

[Larry M.]

Re: Top Hat or High Hat screws on FI

Harry - I'm out of town. When I get back I'll answer the question on length. It is in the 3/4 category but I'll put a caliper on it. Larry

[Mike M.]

Re: Top Hat or High Hat screws on FI

this discussion got my interest so i went to the garage and checked the four 64-65 FI vets that we have. all 16 high hat fasteners are blunt tipped without a cut and all have an embossed "C" centered in a depression in their heads. the early 64, vin 6938, differs from the other FI fasteners in that the two top high hats enter the core support perpendicular to the support(Perhaps by mid-64 model year the General realized that inserting the fastener perpendicular to the support was a PITA so they could have pre-punched the support to allow the fastener to be installed easily at an angle). the other 3 fuelies have their top two high hats entering the core support at an angle. the "C" within the depression required magnification for my old eyeballs to identify them . as far as these 16 high hats being original, i've had the vin 6938 since the mid-80s and it came from barry blocker who got it from the original owner(still alive and an ncrs member). the other 64 FI, vin 21820, has been with me since the mid 90's when i got it from the original owner with 28K miles showing. the 65 vin 5094 i've had since about 1990 and i spoke with the original owner at that time. the 65 vin 9302 has been with me since 1970 when i got it from the original owner. it is unrestored with 20K original miles on it. i can say with almost certainty that these 16 high hats left st louis on these 4 fuelies. over the years as i have junk yarded, i've picked up numerous high hat fasteners, mostly from corsairs as john hinkley and joe ray alluded to in their above posts. after examining what i consider the 16 high hats, i went thru my collection of corvair high hats and all are pointed with the cut parallel to the long axis of the fastener. i might add that as far as judging mid-64 and all 65 FI high hats, the judge will simply need to feel the end of the fastener to discern if its pointed or blunt as the pointed, if massaged vigorously, will bring blood. mike

[Dan H.]

Re: Top Hat or High Hat screws on FI

Mike, 64 Corvettes 13708 and 13901 had the 5/16 screws with 'L' in them. Guess some guys didn't get the memo? Must not of shared their 'stash' of user friendly high hats. Or maybe they screwed the new guys on the line?

[Michael G.]

Re: Top Hat or High Hat screws on FI

GM called "hi-hat" screw heads "high hex washer head" parts.

The most commonly used GM tapping screws had points - without the cutting flute. Those parts are type "AB" tapping screws, but only if they don't have the cutting flute. Pointed ones with the flute are type "17" and they weren't used very often. We usually called them "AB with cutting flute".

The blunt ones are type "B" and they were also pretty rare. They're were mostly used to keep Mikey from slashing his wrists when reaching into dark areas...

[Mike M.]

Re: Top Hat or High Hat screws on FI

mike: what logos appeared, if any, on the pointed high hats? mike

[Michael G.]

Re: Top Hat or High Hat screws on FI

Mike, As John pointed out, the pointed part with the cutting flute was comparatively expensive. This was due to the necessity to machine the flute in a cold-headed part, an extra operation. The cost of this part made it hard to get an engineering change approved when the plant wanted it. This meant that the plant often just mis-used it and ordered lots more than the approved number or brought them in through the back door. Someone's budget covered it, so it it happened all the time....

In the case of the FI part, its such a nightmare to get the non-pointed things into the inaccessible holes, the plant probably just bought the pointed/fluted part because it could find the hole. Once the tip was in the hole the fluted part could then be driven at odd angles and would cut its own path.

Since it apparently wasn't originally a "sanctioned" use on the Corvette FI, small quantity of the parts could have been purchased by the plant from anyone and there were lots of small screw suppliers back then. We've seen an "L" (Lang?), an anchor (Anchor), and "C" (Continental?), but there typically would have been a few more if the plant was mis-using a high-volume Corvair part.

[Larry M.]

Re: Top Hat or High Hat screws on FI

I measured the screws. I have blunt tip and no cutting groove, blunt tip with groove and pointed with groove. All measure 19/32 to 5/8 with the pointed bumping 5/8 most often. As a reference, I have an original 5/16 "L" stamp recessed hex head; it measures 1/2.

[Larry M.]

Re: Top Hat or High Hat screws on FI

I just wanted to thank Mike McCagh for the effort he went to to look at his cars and give his feedback. And I think it is pretty awesome that he has three of these cars.