HP Forum Archive 08

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handheld case screws update Message #1 Posted by Ellis Easley on 31 May 2002, 2:34 p.m. I have another lead on the screws for the handheld cases that we have been looking for. I should get some real Plastite screws next week! I got the #2 X 1/2" plastic thread cutting screws from the website that Paul Brogger pointed out, that had #3 X 3/8 sheet metal screws. The #2's that I got are not what I hoped. They are 32 threads per inch, circular thread like a sheet metal screw, with a blunt end and a notch. I also bought an assortment of small sheet metal screws that unfortunately didn't include #3. I say unfortunately because as soon as I found the #2's weren't what I hoped, I wanted to kick myself for not ordering the #3's to see what they looked like! They sent a paper catalog and I went through it looking for some more items to make up a new order and found listed with sheet metal screws, a #3 X 5/16" with a footnote that said "Servo arm screw Type B - blunt end"! Sounds perfect! However, it doesn't show up on the website and when I asked for it in their search, the system said to call, so I did. I explained to the gentleman what the screw is like that we are looking for and the HP description of the similar screws in the 97 card reader, #2-28, and my belief that the screws are "Plastite". He was familiar with Plastite, said it was a trademark for a patented idea for which the patent had expired and which is made by a number of manufacturers. He said "tri-lobular" is the distinctive feature of "thread rolling" screws of which there are "Plastite" for making threads in plastic and "Taptite" for making machine screw threads in metal. He verified that the #2 Plastite is 28 threads per inch and had a term for the maximum diameter - something like "encompassing circle" - that would be slightly larger than the measure I've been taking with my dial calipers, which for the #2 Plastitie is .089 inch. He also told me the diameter of a #3 sheet metal screw is .102 - .106 inch. In the sheet metal screws that I got, the #2 measure .085-.087 inch diameter and have 32 threads per inch. The #4 measure .113 inch diameter and have 24 threads per inch. It may be that #3 have 28 threads per inch - I didn't get a definite answer on that - but the guy is pretty sure that at .102-.106 diameter they would crack a post intended to take a #2 Plastite. The good news is that he is getting some #2 X 5/16" Plastite panhead phillips screws! They will be zinc plated. They should be just a few dollars per hundred - he couldn't give me a price today but I will call him next week when he will have them in stock. I will order some to make sure they are what we are looking for and post the results here.

Re: handheld case screws update Message #2 Posted by Renato on 1 June 2002, 10:28 a.m., in response to message #1 by Ellis Easley I found this: http://www.ftel.net/~aburg/hp_screws.htm Not much information, but a interesting photo. Renato

Re: handheld case screws update Message #3 Posted by Ellis Easley on 2 June 2002, 8:37 a.m., in response to message #2 by Renato It seems this guy's main interest is the 41 - I wonder if the provision for a longer screw applies to any other models? I'm going to try a "depth gauge" (a length of broom straw) on some of my calculators. BTW, on the page up from the linked page, the guy says he has some 41 parts to sell - give him a few days to put them up - page last updated: 6-4-98!

Re: handheld case screws update Message #4 Posted by Renato on 2 June 2002, 11:19 p.m., in response to message #3 by Ellis Easley Yes, 5+ years old information - but useful anyway - digging the web fossiles can be as useful as digging used books stores. And at the end of the day your clothes are clean. BTW this is a great forum - let's keep spirits up.

Re: handheld case screws update Message #5 Posted by David Smith on 1 June 2002, 4:07 p.m., in response to message #1 by Ellis Easley Did you order any of the #3 servo screws or did they say if they had them or could get them?

Re: handheld case screws update Message #6 Posted by Ellis Easley on 2 June 2002, 7:57 a.m., in response to message #5 by David Smith I'm afraid I didn't order any #3's in my original order. I'm going to get some when I place my order for the Plastites, after he gets them in stock next week. I want to see them and have them on hand, plus I want to get more for my $5 shipping charge! The #3 X 5/16 were not orderable via the website, even though I had the catalog number from the paper catalog. When I called, I never asked him specifically about those screws - I was so happy he knew what Plastite screws are! But I have a note to ask more questions and order some #3's when I talk to him again. I'm especially curious to see if 28 is the normal thread pitch for #3, since #2 are 32 and #4 are 24.

Re: handheld case screws update Message #7 Posted by David Smith on 2 June 2002, 4:42 p.m., in response to message #6 by Ellis Easley I checked my HP screws with a caliper and they are 0.087 diam. with between 24 and 30 threads/inch depending upon the vagaries of measurement. So it looks like they may indeed be #2-28. The HP97 reader screws match the normal HP calculator screws. The #2's that I originally compared them to are apparently some weird or metric #2's that have a different diameter and pitch. I found some other #2's (different pitch than HP though) that do match the HP diameter. The HP screws all have the type "B" (blunt) point. A few do have a small "V" notch in the tip, but this is not the norm.

Re: handheld case screws update Message #8 Posted by Ellis Easley on 3 June 2002, 7:35 a.m., in response to message #7 by David Smith When I was on the phone with the guy, he started to explain why sheet metal screws come in two (or more) thread pitches for the same basic screw size. That's one thing I'm going to ask about again, and take some notes. He agreed that in an actual sheet metal application it doesn't really matter what the exact thread pitch is since you're cutting only about one turn of the thread in the material and if you put a screw with the other thread pitch in a previously threaded hole, the metal will bend a little to accomodate it. I think it is interesting that in machine screws, only #10 has two common thread pitches (24 and 32). I think the Plastite screws (if that's what it turns out to be) always have a blunt tip which is slightly tapered to make it easier to start. The typical application is in a hole molded in a plastic part with the bottom of the hole flat. A pointed tip could damage the thread if it stopped the screw going in when the tip hits the bottom, or worse, it could poke through or cause a bump on the outside of the molded part. Also with a blunt tip you get threads all the way down the hole (as far as the screw goes, anyway). One more thing I'm going to ask about is hole sizes for Plastite screws. In addition to the #2's I'll be getting, I have #6 and #8 in my junk box. I imagine the ideal hole size depends somewhat on the material. My Pocket Ref book has a page on sheet metal screws and gives hole sizes which depend on the thickness of the metal. Also has a footnote: "Variations in materials and local conditions may require significant deviations..."

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