Looking for 8-32 flat-head with hex... not phillips

[high plains drifter]

Fastenal should have an extensive selection of 8-32 stainless and oxide hardware. If you were closer I'd hand you some! I've got a bunch of the stainless stuff on hand in button head and countersunk that all use a 3/32" allen.

I appreciate it and yep... At this point I've found ( with the help of others in this thread) lots of places have what I need technically.. Bolt Depot, Monster, Fastenal, Grainger, even Amazon to an extent. The issue is that none of these flat-heads ( hex-head in black oxide or stainless) fit perfectly flush in this particular application. They're all chamfered/ angled too steep or the heads themselves are simply too large.

 

[svt923]

Based on info I found on some vintage RC forum, the RC10 chassis screws are the less common 100 degree countersink type of 8-32 screws.

McMaster has a pretty good selection of hex heads in that configuration:

100 degree flat head 8-32 screws

 

[89Industries]

Just thinking out loud here:

8-32 flathead screws have an 82 degree angle.

Metric uses 90 degree. So metric hardware would sit even higher.

But lots of countersink tools are really for use as a center drill and have 60 degree angle. Not meant to fit a flathead screw but meant for locating the thru drill more precisely or for using a live center on a lathe. Not to fit hardware.

I wonder if they just screwed it up back in the day and used a 60 degree countersink. In the 90s you had to look crap up in big catalogs with tiny print or generally I feel it was just easier to make mistakes or not be able find exactly what you're looking for so you made do.


If that's the case then you could use an 82 countersink to fix the angle without making the countersink deeper.

How to measure and figure it out without buying stuff I don't know.

Have you measured the diameter of the countersink hole at the surface? Would need a caliper and still have to just get close since there's nothing for it to clamp on to and measure.

I still think Phillips machine screws with the smaller of will be the closest. Or those Torx bolts with a .290" diameter (Phillips machine screw size) head from Amazon if they really measure as they say they do.

Sorry for loading you down with info. I'm probably thinking about it more than you but my head loves solving stuff like this.

 

[Lashlee]

I'm sure I had bags of those screws in the early 90's from the RC-10LSS pan car or from my Losi JR-X2 and XT, then XX and XX-T when you had to bring everything with you since the hobby shop wasn't next door to the track!

 

[high plains drifter]

@svt923 - I'll take a look at McMaster... One of the only places I haven't looked yet. And I wasn't aware of these rc screws typically being under 100 deg so that may be a significant part of the puzzle here. Being that chassis plates are fairly thin ( this one is 3/32 in. and the original tub-chassis even thinner than that) maybe Associated was forced to utilize a flat-head that was not so conventional. Finding replacements for the smaller flat-heads on this chassis haven't been an issue but these 8-32's are another story. Much appreciate the link.

@89Industries - Not at all. Can't express my appreciation enough. But that said, there's a point where I have to kind of slow down here because I can't simply "trial and error" everything out there due to feasibility. I haven't measured the holes btw.

I believe what they did here was intentional because the chassis plate is so thin that most conventional 8-32 flat-heads won't fit flush without [maybe] compromising the overall strength of the part ( union of parts)... like if they would've had to have made the countersunk holes that much deeper to accommodate the more widely available flat-head options, then they would've also had to have either made the chassis plate thicker or would've had to have countersunk further into the plate... subsequently giving that screw-head very little real-estate to secure to. I haven't checked since I don't have flat-heads to compare, but I assume that the depth of most of these heads are probably thicker than most chassis-plates themselves... which again would explain why they chose ( or manufactured specific propriety) the particular hardware that they did. Cost might've also been a reason that they chose aluminum over stainless and phillips over hex but I dunno... just a guess.

Going to look at McMaster now while I assume my wife will be entertaining divorce proceedings.

 

[89Industries]

The thin plate and 100 degree angle countersink and flatheads would make total sense in this application, but looking at the pictures earlier in this thread, the countersink holes have a small diameter at the top surface. That makes me think of smaller angle like a 60 or even the 82. So I hadn't even considered that it would use a 100 degree flat head.

Looking at the 100 degree flathead screw dimensions on McMaster, they have the same OD as the standard 82 degree flathead socket head screws, so they may sit a bit closer to the surface, but they will still protrude above the surface since the head is larger than the large diameter of the countersink (I am taking this from the picture earlier in the thread that showed all the different flat heads, sae, metric and phillips, and all the heads were larger than the top large countersink diameter).

If they used a 100 degree countersink tool to match a 100 degree flathead screw properly during manufacturing then the countersunk hole should be flatter, shallower and the diameter at the top of the countersink should be larger than they appear to be.

So I forget that my brain is very good with spatial visualization in a way not everybody is. I agree at not throwing parts at it in a trial and error fashion, but I don't want to go through the geometry problem here unless you want me to. You can PM me and I can draw out the diagrams and all that or tell me to just post it here. I would be happy to help either way.

A set of digital calipers will help a lot to take the needed measurements. The cheapos from Harbor Freight work well enough and are reasonably priced if you don't already have a set. And since they are a tool that could help you buy less stuff in the future they will likely go over ok with your wife.

Also, (warning, a bit off topic rant) McMaster is awesome for finding stuff, part dimensions and if you use cad, getting files of nuts and bolts so you don't have to create them all yourself. My complaint is that they now seem to have a $10 minimum shipping and it seems to go quickly up from there as you add items. So when I need $4 dollars of bolts the shipping kills it. They are not usually the cheapest option for stuff either so where as I used to order metal stock, hardware and any specialty tools all from them, now I find it cheaper to get them from separate sources and can usually save $20-30 on a project. Doesn't seem like much but it adds up. Kind of a bummer.

 

[high plains drifter]

@89Industries - Yeah, I just noticed on the chassis that I have that there is indeed a tiny recess rather than the angle simply being chamfered right up to the top of the plate. This recess or step is minuscule but with the correct size head, it would assure that the screw sit perfectly flush. Not sure if I'm making that clear lol.

Diameter of the hole right where it meets the surface of the plate is .317 in ( 8.06 mm). The factory screw head OD is .295 ( 7.49 mm). Those are the phillips head aluminum screws. I did also happen to find in one of my parts bins, a few stainless 8-32's that are hex-head and have a head dia. of .313 in ( 7.96 mm) but they don't fit perfectly flush on this chassis... close but not completely flush. They would possibly work but unfortunately I don't have the quantities or lengths that I need.

Looking closely at them I can see that the angle or chamfer is steeper than the factory aluminum ones so makes sense why they don't fit exactly flush. No idea where they originally came from... might have been through a LHS, maybe even AE but they definitely didn't come from a box store. Keep in mind that this was all from about 25+ years ago lol.

I've got a good set of digital calipers that I couldn't live without and innovating/ modifying/ fabricating is nothing new to me but this holy-grail 8-32 thing slowed me to a crawl on this particular project. And I really do need a thread-pitch gauge.. don't know how I've gone so long without one but I may pick one up this weekend since I have a lot more hardware to replace on this job.

I appreciate the offer to go into this further in depth but I'm just going to look around a bit more... still have check out McMaster but I got busy yesterday and had to temporarily suspend my search.

 

[Gula]

How about an m3 thread inseart melted into the plastic part and an m3 flat head? Would sit flush. Here's what I did using one of those small chuckable deburring bits:

Rc10ds


Furthest outside holes
Tool i used for the m4 hardware. I also countersunk the plastic a bit.

 

[high plains drifter]

Thank you, Gula. This is why I need a thread-pitch gauge. Some of these screws will be threading into aluminum parts on the top side of the chassis... like the rear bulkhead for example. The original is plastic but I'm using an after-market alum bulkhead so threads will have to match. Another issue with deepening the holes is that there's a couple areas ( rear a-arm mounting blocks) where the holes are already very close to the edge of the chassis... only 1/ 32" ( .67 mm) from the edge. I'd risk potentially enlarging those holes past the edge of the chassis.

 

[high plains drifter]

Just to update this- I just spent $70 on 20 screws so for any of you with a spare bedroom or even a warm corner... maybe next to a fireplace, I may need a place to stay.

They haven't arrived yet but McMaster Carr I believe is going to save me on these 8-32's. Only drawback... assuming that everything is correct, is the expense. What I ordered were 10 ea 1/2" and 3/8" stainless/ flat-head/ hex-drive/ 8-32. There was no thread choice so hopefully that won't be an issue. And I did order more than needed so not sure if I'll digest this cost or send back what I don't use but McMaster Carr's return policy seems very hassle-free.

Related- My Team KNK hardware came in and looks great. Unfortunately ( but as expected) the 8-32's were Phillips-head. I did also get a bag of 8-32 stainless/ hex-head from KNK but also as expected, the head angle does not allow them to be fully countersunk. Not a huge deal and I don't think I'll send them back because the cost wasn't that much. And they do come close to being fully countersunk... just not quite there.

Now, on the KNK stuff I will say that I went ahead and also ordered ( separately from the specific RC10GT bag) two bags of Phillips head 8-32 gold flat-heads... the original ones that came with these trucks. Not what I wanted with the Phillips and aluminum specs but figured if I ultimately had to, that I'd at least have all the original hardware. On this project I am trying to make some upgrades as I go and although I never had one of the original aluminum 8-32's break, the Phillips-head slots really took a beating. Hopefully with the McMaster Carr flat-heads that will be here in the next few days, I'll finally have a complete set of stainless/ hex-head hardware.

What a royal PITA this has been lol but to those who have offered their expertise and advice here.. .I can't thank you enough.