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In 2009 ZDP-189 blade steel was the hottest, hardest and highest performing Japanese knife steel in the knife industry. 3% of its component ingredient is pure carbon and 20% chrome (unheard of chemistries twenty-years ago), making the steel harder and in turn extending its edge retention. This is done through a powdered metallurgic process. At the time of MT04P Mule's release, Spyderco was one of a handful of cutlers around the world working with ZDP-189 blades.

MT04P ZDP-189 Mule was originally released in a very limited quantity due to unforeseen issues. The Mule Team project was created to give more people access to various steels using a standard pattern for a fixed blade knife. The hope of the project was to find out what these steels can do by making them available at an affordable price for our Knife Knuts and Steel Junkies. We test our products constantly, but we’ve always maintained that no amount of “testing” can provide the information that real-world use can.

With the ZDP-189 Mule our goal was to reach the optimal hardness that we had in our folders (in 2009 as well as presently). Shortly after the release of MT04P it was discovered that the optimal hardness is different for a fixed blade. Once this was discovered Spyderco placed a hold on shipping any additional MT04P Mules.

The Mule Team is a project based upon the desire to learn more about different types of steel and the performance of each steel. The scenario with the MT04P Mule, although not planned, certainly provided some previously unknown and valuable information into one of our industry’s most exotic steels.