They were routinely sold under the name &quot;MacCracker&quot; - and had a flat disk with a ridge.  Once the screws were out, the ridge would be worked as a lever to separate the edges.<p>Bottom has some screen shots:<p><a href="http:&#x2F;&#x2F;www.tcocd.de&#x2F;Pictures&#x2F;Micro&#x2F;Apple&#x2F;mac128.shtml" rel="nofollow">http:&#x2F;&#x2F;www.tcocd.de&#x2F;Pictures&#x2F;Micro&#x2F;Apple&#x2F;mac128.shtml</a>