At 12:07 +0100 6/29/04, Susan Platter wrote: >This is all helpful stuff, thank you. I've been offered a dead SE, so was hoping to >be able to reuse the chassis screws at least. I didn't understand the reference to >"sheet metal" and "4-40", though. Can you please translate for the technically >challenged?
Sheet metal screws have sharp threads that look a bit like a wood screw. The idea is that one punches a round hole in the sheet metal and then forces the screw in. The screwing action deforms the sheet metal so that it conforms to the shape of the screw. With repeated insertion the sheet metal wears out and a somewhat larger screw is required for a firm replacement. Some designs use sheet metal nuts, sometimes called Tinnerman nuts, which snap onto the sheet metal to allow for reuse. The pitch of sheet metal screws varies all over the lot and it's fairly important to find a replacement that is close to the pitch of the original screw. That avoids unnecessary damage to the sheet metal. 4-40 NC or 6-32 NC are US designations for machined screws which have flat topped threads and require a pre-threaded hole or a nut. The first number is a size designation. larger numbers are for bigger screws. The second is the number of threads per inch. There are NC (national coarse) and NF (national fine series). A 6-40 is a NF screw. Incidentally, those hard disk screws are 6-32 and not 4-40 as I once said. Metric screws are identified by their diameter in millimeters and their thread pitch as millimeters per thread. A 6-1 metric screw is 6 mm outside diameter and each thread is one millimeter from its neighbor. The tops of the threads are rounded rather than flattened as in US standards. A problem with metric screws used in computers is the strange multiplicity of "standard" sizes. One can buy both 3-0.75 and 3-0.7 metric screws, for instance, in different countries and it's nearly impossible to tell the difference by looking at them. I was once involved with a product being sold to Aero Vodochody (Czech aircraft). They insisted that we replace our 4-40 NC screws with "M3". "Which M3" I asked. "Standard M3" they said. "Which standard?", I asked. And on it went. They finally had to send samples to us. -- --> If you are presented a number as a percentage, and you do not clearly understand the numerator and the denominator involved, you are surely being lied to. <-- -- Compact Macs is sponsored by <http://lowendmac.com/>. Support Low End Mac <http://lowendmac.com/lists/support.html> Compact Macs list info: <http://lowendmac.com/lists/compact.shtml> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive:<http://www.mail-archive.com/compact.macs%40mail.maclaunch.com/> --------------------------------------------------------------- >The Think Different Store http://www.ThinkDifferentStore.com ---------------------------------------------------------------
