On May 30, 2009, at 7:54 PM, Arnel Tuazon wrote:
> I just noticed that the G4 Gig-e Mac I have has a problem with 2 of
> the hard
> drive plates. You know the metal plates that you attach the hard
> drives to
> and then in turn attach these plates inside the bottom of the G4
> case. Each
> plate has one screw that keeps it in place inside the case. I
> noticed that
> the screw for 2 of the plates has been damaged. The head of each
> screw has
> been damaged to the point where no screw driver bit could ever
> snugly fit
> into it to allow you to unscrew the plate.
>
> Anyone know how to get the screws out? As of now only the center
> hard drive
> plate can be removed the others are stuck with the damaged screw
> heads.
The rear-most drive mount, the one which accepts two drives in a
stacked configuration, requires special thin head screws.
The screws themselves have a #6-UNC thread, which is a coarse thread
(UNC means "Unified National Coarse"; there are indeed UNF threads,
"Unified National Fine").
The threads are NOT fine, which on a Mac generally means M3-0.5,
metric, 3.00mm dia., 0.50mm thread pitch.
Optical and Zip drives are the only drives within the desktop and
mini-tower series of 60x, G3 and G4 Macs which are mounted using
metric fasteners. The hard drives are always mounted using #6-32 UNC
("Imperial") fasteners.
These thin head fasteners are quite special, and were made for Apple
to its specifications.
The single-high drive carrier can use conventional head #6-32 UNC
screws; it is only the two-high drive carrier which requires the
special thin head screws, and even then, these special screws are
necessary only when mounting the drive from below.
If mounting the drive from the sides, then conventional #6-32 UNC
screws may be used.
Now, the drive carrier itself is mounted to the base of the mini-
tower by screws which _appear_ to be the same as the drive mounting
screws, but _these are not the same_; these are M3.5-0.6, metric,
3.50mm dia., 0.60mm thread pitch.
M3.5-0.6 fasteners were adopted by Apple in 1984, with the
introduction of the very first Mac, the 128K.
However, in the very same year, 1984, the M3.5-0.6 fastener size was
abandoned as a standard by those countries which endorsed, or
mandated metric standards.
Consequently, most M3.5-0.6 fasteners are custom made for Apple. No
one else that I am aware of uses M3.5-0.6 fasteners in their products.
Historically, M3.5 is just about the same diameter as #6, so an M3.5
fastener has just about the same shear strength as a #6 fastener.
However, in the post-1984 metric standards, there is no standard
fastener size between M3 and M4, and M3 has too low a shear strength,
while M4 has too great a shear strength, for many mounting applications.
Hence, although it may be "archaic", from a metric perspective, to
use #6 fasteners for hard drives, this size is still the standard,
world-wide.
Now, as to the PCI/AGP/PCI-E card mounting screws ...
The world-wide standard is also #6-32 UNC.
However, in order to keep its products as "all-metric" as was
possible, Apple deviated from the card mounting standard and used
M3.5-0.6 fasteners there, too.
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