On 19/01/2012 23:48, Justin wrote: > On Jan 19, 2012, at 13:25 , Gerrit Heitsch wrote: > >> On 01/19/2012 02:27 AM, Justin wrote: >> >>> Be aware that thread pitches are different for metric and US screws, and that due to manufacturing variability and tolerances, screws that technically have the same thread pitch may still fit slightly tight or loose. The 64 probably uses screws made to US specs rather than metric. >> They probably designed it US screws since that part was done in the USA. But when it came to making it, I'd say the plants used whatever was available locally and fit. Remember, the C64 was made all over the world including Germany, Hong Kong and the UK. On first insertion, the screws cut their thread into the plastic of the case so there is no need to get too specific. >> >> Gerrit > Sure, but since he is putting in replacements (presumably), having the same thread pitch and diameter will preclude tapping new threads into the now rather ancient plastic. It probably doesn't matter too much, since Commodore seems to have used fairly decent plastics that mostly haven't gotten brittle with age, but since it costs almost nothing to get it exactly right, why not get it exactly right. > Message was sent through the cbm-hackers mailing list Thanks for all the input chaps. I sourced some screws 2.9 x 9.5 from the local Hornbach and the thread matches > 70 % of the pre existing tapped holes in ABS plastic in C= 8-bits. Most of my kit was manufactured in the UK, Germany or the far east. I probably do have US manufactured stuff but couldn't immediatly lay my hands on it. One observation is that a thread length of 9.5 mm is too long for holding the MB to the bottom shell on the 64 & plus/4. It noticeably deforms the plastic on the underside of the shell. Having looked at the alternatives, 6.5mm screws seem to be the next smallest standard size available. There is now a DIN and ISO standard for the type of screws required; DIN 7981 / ISO 7049 which defines standards for 'Cross Recessed Pan Head Tapping Screws' - nice! Rob Message was sent through the cbm-hackers mailing listReceived on 2012-01-20 00:00:14
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