e91e9179_Oscillating_tools___DIYWiki__Blade_Mounting
[Machine] Original Fein Multimaster [Blade Mounting] 
The original Multimaster used a basic screw fixing for the blades without any further registration lugs or pins. The blades simply had a 10mm mounting hole that sat over the flange on the tool post, and the fixing screw with clamp plate tightended down onto them. This system allowed the blade to be installed at any angle. However it does require the screw to be securely done up with the supplied allen wrench, or the blade position can wander in use. One advantage of the earlier Fein machine mounting is that it allows use of all the various blade designs available.
Oscillating tools - DIYWiki
Blade Mounting