As long as your keys are flat and have a hole larger than 3mm, they will fit the Keystone.
For reference, see the keys that I use in my own Keystone:
The Steel Keystone has stainless steel frames.
The Raw Keystone has raw aluminum frames.
The Gunmetal and Black Keystones have hard-anodized aluminium frames.
The screw posts and spacers are stainless steel.
Steel Keystone frames weigh about 1.54oz (44g).
Raw, Gunmetal and Black frames weigh about 0.53oz (15g).
The hardware to hold up to 4 keys are about 0.28oz (8g).
The hardware to hold up to 20 keys is about 0.74oz (21g).
Due to the absence of anodizing, the Raw Keystones are scratch-prone but very reflective/shiny.
The Steel Keystones are somewhat scratch-resistant. They can be compared to kitchen utensils.
The Gunmetal and Black Keystones are hard-anodized and extremely scratch-resistant.
The Keystone holds all flat keys perfectly.
The Keystone comes with a key-ring and carabiner set-up that allows you to attach odd-shaped keys like in this picture: http://i28.photobucket.com/albums/c218/jqang/Project%20Key/20140928_210727.jpg
The base pair of screw posts hold about 1/2" (13mm) of material.
The extension posts hold about 3/8" (10mm) of material.
A typical key is about 2mm thin.
The frames are each 2mm thin.
The spacers are each 1mm thin.