The Warehouse in the Industrial Design building loans out a variety of tools to students and specifically to this entry, end-mills are loaned out for the metal shop machines. As an example, the mistake that I have observed has resulted in broken end-mills and increased the potential for injury.

As they are cutting into the material, SNAP! goes the end-mill, and hopefully everyone in the vicinity has their eye-protection on. 

Was it a mistake? Perhaps a memory-lapse mistake, the student may have not installed the tool correctly in the machine due to being distracted in a conversation with a friend. This is also a rule-based mistake, as the shop policy states that every student has agreed to include not being distracted using the machines.

Could it have been a slip as well? Likely also a memory-lapse slip, even if alone in the workshop, one step of the procedure could have merely slipped their mind.  

The most significant mistake is as follows, a regular confluence of errors. It goes like this: the student needs to borrow an end-mill from the tool crib, students are frequently inexperienced in using the tools, have only a limited understanding of terminology, and perhaps even have a language hurdle. They make their verbal request, are given a tool, and off they go. SNAP! 

This time they were given the incorrect tool. This could be a rule-based mistake on the part of the technicians working in the tool crib, and perhaps a knowledge-based mistake on the part of the student. The student did not request the correct tool, and the technician did not verify that they provided the correct tool.

Better reasoning needs to be applied at the point of tool delivery in my opinion. Deductive reasoning applied to a conversation (a brief series of questions) that the technician begins when the student has a tool request. Deducing, from the series of answers, what exactly the student needs, as well as, potentially how experienced the student is. This conversation could potentially act as a constraint to prevent incorrect tool acquisition and in turn, prevent incorrect tool usage.