Arrive with an idea, leave with a 3-year plan. Achieve reliability.

TRC gives you access to cutting-edge knowledge & technology

Sign Up

Please use your business email address if applicable

Wrench time, or tool time as it’s called in some countries, is an often touted measure for determining maintenance productivity since it’s intended to measure the actual time technicians spend working with their tools at a given job. Typical numbers observed are 25 to 35 percent, meaning technicians typically spend 65 to 75 percent of their time not working or, at least, not getting the work assigned done. Is this a valid measure or conclusion? Is it useful to measure wrench time? The answer is yes, if properly done, as well as a resounding no, if not properly done, which happens more often than not!

Typical numbers observed are 25 to 35 percent, meaning technicians typically spend 65 to 75 percent of their time not working or, at least, not getting the work assigned done

Measurement Techniques

There are two basic ways to measure wrench time. One is work sampling, wherein an analyst with a clipboard and a chart broken into 10 to 15 minute intervals observes technicians and determines whether or not they are working on the job. Not working typically has to do with traveling to and from the job site; waiting for parts, permits, access and tools; waiting for start-up checks; and taking part in other activities, such as receiving assignments and instructions, taking breaks, going to training, closing out work orders, attending administrative meetings, or anything else where actual work on the job is not being done. It’s important to understand that most, if not all, of these activities are or can be essential, but the key is to minimize the amount of time on these activities, while maximizing the time for getting a quality job done.

The second technique is a day in the life of (DILO) a maintenance technician or operator. This approach tends to be more enlightening because you spend more time talking with the technician and getting a much better understanding of the day-to-day obstacles and frustrations.

DILO Case Study

At a power station in the United Kingdom, a reliability consultant planned a DILO with a maintenance technician (called a “fitter” in the UK). Upon introductions, it was clear the fitter was suspicious of the consultant. The fitter asked numerous questions, among them: Why is that? What do you intend to do with your observations? Will I get to see them? The technician was assured that the consultant would NOT be checking to see if he was working, but rather looking for things that were stopping him from working. While the consultant was confident the fitter and all his mates wanted to do a good job, the focus of the DILO was on answering the question: What was preventing that from happening?

This is a critical point in measuring wrench time. If your objective is to see if people are working, they will become very suspicious and not be very cooperative. Indeed, they will be fearful of your objectives. On the other hand, if they view the process as being one to help eliminate their frustrations and obstacles, they will be far more likely to cooperate and be very helpful. Far too many people do work sampling with a view of checking on whether people are working instead of looking for the obstacles that prevent the work from getting done.

At the UK power plant, the maintenance technician stood and waited for about 15 minutes for a work order with his job assignment. He finally received the work order from his supervisor, which directed him to replace the gasket on a filter of a ball mill. Its function is to pulverize coal before it gets blown into the boiler. Of course, the job required a gasket, so the technician, along with the consultant, went to the storeroom, which, fortunately, was nearby. The two stood in line for another 15 minutes. After receiving the gasket, they traveled to the mill, taking another 10 minutes. On arrival, the mill was running, so the gasket couldn’t be changed. They then went to the control room and asked about shutting down the mill. This required a permit and the machine to be shut down, locked out and tagged out. This took another 45 minutes. All the while, the fitter and consultant were waiting. The consultant asked the technician if this happens often. He responded, “Most every day.”

The consultant asked the technician if this happens often. He responded, “Most every day.”

When the fitter finally had access to the mill, he proceeded to remove all the bolts holding the gasket in place. The consultant even helped with an extra wrench he had, which was much appreciated. This took about 10 minutes. Unfortunately, the storeroom had given the fitter the wrong gasket, so he and the consultant returned to the storeroom, with measurements in hand, and finally received the correct gasket. Another 30 minutes had passed getting the correct gasket. The maintenance technician then put the correct gasket on the mill. This took about 10 minutes. Next, he and the consultant went to the control room to get the mill restarted, which dictated that an operator had to untag, unlock and restart the mill so the fitter could check the gasket to make sure there were no leaks.

The operator went through the process, but as soon as the mill started, it tripped. He opined that he hadn’t started the mill in six months and went to get the start-up procedure. On returning, he observed that he hadn’t shut (or opened) a valve that should have been. Once he followed the procedure, the mill started right up and, fortunately, there were no leaks. However, another hour had transpired while waiting for the operator to start up the mill. Finally, the job was over and the fitter and consultant headed back to the supervisory area to close out the work order. Another 15 minutes transpired. Then, they went looking for the supervisor to get another work order, which took another 15 minutes. This time, the work order was to change the gasket on a steam line. Needless to say, the fitter had to go through the same process for this job.

During the DILO, the fitter did 20 minutes of actual work, meaning wrench time or tool time, but about 3 1/2 hours passed getting this done. Wrench time was about 20 minutes divided by 210 minutes total time spent, or about 10 percent. Should the technician be fired for working only 10 percent of the time? Clearly not. What should be done to improve his day? Planning and scheduling would help – assignments are done on the day prior. Planning would include coordination for permits and making sure the right gaskets are specified. Planning that included kitting the gaskets and placing them in a staging area would also help. Having the operator actually use the start-up procedure also would help.

Note that other non-wrench time, such as training, administration, breaks, etc., is not included in this tiny case study.


Measuring wrench time can be a very effective means of improving productivity if it is done with a focus on removing the obstacles and frustrations that prevent the work from being done efficiently and effectively.

Wrench time should never be used for checking to see if people are working. It’s important to assume that people want to do a good job. You have to help them be able to do that and not blame them when they don’t. If you want to understand the problems with getting the work done, ask the workers and work with them to resolve or mitigate those problems.

Ron Moore

Ron Moore is the Managing Partner for The RM Group, Inc., in Knoxville, TN. He is the author of “Making Common Sense Common Practice – Models for Operational Excellence,” “What Tool? When? – A Management Guide for Selecting the Right Improvement Tools” and “Where Do We Start Our Improvement Program?”, “A Common Sense Approach to Defect Elimination,” “Business Fables & Foibles” and “Our Transplant Journey: A Caregiver’s Story”, as well as over 70 journal articles.

Ron holds a BSME, MSME, MBA, PE, and CMRP. He can be reached at

ChatGPT with
Find Your Answers Fast