Why wrench time can be a terrible metric

Jan. 5, 2022
Doc Palmer says if you’re not factoring in breaks, meetings, and storeroom trips, wrench time data can trip you up.

Wrench time is a popular subject about a tricky metric. In the Maintenance Planning and Scheduling Handbook, I state the sixth principle of planning as “Wrench time is the primary measure of workforce efficiency and of planning and scheduling effectiveness. Wrench time is the proportion of available-to-work time during which craft technicians are not being kept from productively working on a job site by delays such as waiting for assignment, clearance, parts, tools, instructions, travel, coordination with other crafts, or equipment information. Work that is planned before assignment reduces unnecessary delays during jobs and work that is scheduled reduces delays between jobs.” But wrench time can also be a terrible metric and probably best left unmeasured!

Let’s begin with an example of wrench time. We consider the activity of actually turning a wrench on a job by a mechanic to be so-called “wrench time” because the job is moving ahead to completion. But if the mechanic has to leave the job for a few minutes to walk across the plant to get another gasket and return, that is not “wrench time” even though getting the gasket was essential to completing the job. We “wish” the mechanic had already had the extra gasket and did not need to travel to the storeroom, wait at the storeroom, and return from the storeroom. Getting the gasket is “work,” but it is not “wrench time.” These definitions are really picky.

The concept matters because valid statistical studies show wrench time is only 35% for typical company workforces. On the average, craftspersons are only actively moving a job ahead about 3½ hours out of an entire 10-hour shift. It means that 65% (or 6½ hours) are “not productive.” (And a study does not even include time away for vacation or training.) Obviously breaks are not wrench time even though a necessary part of the work day. Two breaks at 15 minutes each are 5% of a 10-hour shift. A 15 minute shift check-in meeting and 15 minutes at shift end to clean up add another 5%. Breaks plus check-in and wrap-up alone consume a total of 10% of the day. Hard to believe, but walking to and from the break room, job, tool room, and storeroom; waiting a few minutes at the tool room and storeroom; and being idle for a bit during jobs or between jobs and some time waiting for others to clear equipment consumes the other 55% unproductive part of each day!

All these little things add up. And at the same time, we bend over backwards to give credit for productive tool time, wrench time. We give wrench time credit for any person at a job site even if only one person is turning a wrench. We give credit for the confined space guard, for helping with lockout/tagout, and even troubleshooting on or off the jobsite. We also give credit for filling out paperwork before or after a job (the feedback especially being valuable and not ever considered a delay). We want the final results of a study to show if direct tool time is only 35% in spite of counting nearly everything that could possibly be considered productive time. Surprisingly, most companies have productivity plateaus at about 35% because at that point humans “feel” busy. All of us have this true opportunity to improve.

About the Author: Doc Palmer

I consider best practice wrench time to be only about 55% which brings a huge plant benefit. The 55% does not seem like a lot, but consider: 55 (new wrench time) divided by 35 (old wrench time) equals 1.57. That means we get a 57% improvement in work order completion rate. Let’s call it a 50% pop. That means if we were completing 1,000 work orders each month, we will now be completing 1,500. If we had 100 craftspersons, it would be like we now have 150.

And the benefit does not stop there. The industry rule-of-thumb for proactive maintenance is 1:10 meaning every extra $1 spent on proactive maintenance is worth $10 on the bottom line. (An example is spending an extra $1 proactively greasing a bearing instead of reactively replacing a seized bearing with collateral damage and loss of product.) And the 50% extra is new proactive work which answers the management question: “How can we do extra proactive work when our hands are full of reactive work?” The monetary benefit is illustrated by a 100-person workforce paid $50 per hour for an annual payroll of $10.4 million (100 × $50 × 2,080 hr/yr). A 50% pop in staff is worth $5 million in extra labor put toward extra proactive work. The 1:10 rule gives the value of $50 million in annual plant profitability.

Nonetheless, wrench time can be a terrible measure! It does not measure if a person is doing a job efficiently or even doing a job that needs doing! Consider a craftsperson working on a pump trying to install the wrong bearings. The craftsperson works directly at the pump all shift without ever checking in, needing extra parts, or even taking breaks. Additionally, the craftsperson has mistakenly taken the wrong pump out of service to repair. The person has 100% wrench time that day doing the wrong job in the wrong way! Even so, we presume that all other things are the same before and after wrench time improvement. If we generally assign the correct work and work correctly, we will complete more correct work correctly.

Furthermore, measuring wrench time does not improve wrench time. If we simply measure wrench time without doing anything else, craftspersons just try to “look busy” without necessarily completing more work. Even focusing on the work completion rate doesn’t help improve wrench time because persons might take short cuts to improperly complete work orders faster. We do not want either of these behaviors. We honestly want to complete more valid work orders properly. And proper planning and scheduling help improve wrench time. So we must focus on properly planning work and scheduling work to improve wrench time.

The concept of (not necessarily the measuring of) wrench time shows we have a great opportunity to get a 50% pop in work order completions! As the sixth principle states “…Work that is planned before assignment reduces unnecessary delays during jobs and work that is scheduled reduces delays between jobs.” Start or redirect a program of great planning and scheduling. Be a great plant!

This story originally appeared in the January 2022 issue of Plant Services. Subscribe to Plant Services here.

Palmer's Planning Corner

This article is part of our monthly Palmer's Planning Corner column. Read more from Doc Palmer.

About the Author

Doc Palmer | PE, MBA, CMRP

Doc Palmer, PE, MBA, CMRP is the author of McGraw-Hill’s Maintenance Planning and Scheduling Handbook and as managing partner of Richard Palmer and Associates helps companies worldwide with planning and scheduling success. For more information including online help and currently scheduled public workshops, visit or email Doc at [email protected]. Also visit and subscribe to

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