Examples 51-60

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Examples 1-10

Examples 11-20

Examples 21-30

Examples 31-40

Examples 41-50

Examples 51-60

Examples 61-70


uk plug

British 240v/50Hz electricity can injure people so electrical plugs are designed so that live electrical pins are never exposed.

1. the pins’ position and orientation are such that the plug can only fit one way in the socket
2. the pins are insulated near the plug body so that electric shock is not possible via the exposed pin if the plug is not pushed all the way in but still
making contact. 



This clever idea is not a mistake-proofing device in the purest sense.  However, rapid feedback is a guiding principle in mistake-proofing and this switch in a discount store restroom seems to fully exemplify that idea.












shave ice

shave ice








Rival sells a shaved ice machine that spins the ice around, pushing the ice over a blade which shaves it into snow cone “snow.” Rival is very interested in NOT shaving any fingers. They have designed the “on” switch into the lid. You press on the lid to activate the machine. When you stop pressing the lid the machine stops rapidly. The tabs shown on the lid in the picture (above right) press switches beneath the small holes (one shown with the larger arrow).  You physically cannot have your fingers in the mechanism and turn it on at the same time (unless you are a masochist with a pocket knife or small screw driver). 



Blockbuster has figured out that helping customers get their videos back on time is good for business. This is another example that does not mistake-proof the process but does help customers get it right.  If every process we interacted with did as well, the number of mistakes we make would be dramatically reduced .





What could be better than a mistake- proofing device that increases sales by creating a niche in a commodity product category?

Crayola is selling markers that don’t write except on special paper. No more blue, green, and red fingered toddlers. No more ruined clothing. Nice mistake-proofing. Masterful marketing. GE essentially gives jet engines away in order to get 20 years of reparts business. Perhaps Crayola should give away the markers to get the specialty paper sales.

Can you think of an industrial use of this technology?


















 abc tray

Even fancy sandwich shops can’t afford to have their trays discarded.  Preventing customers from making a mistake, in this case, means making the trach can opening smaller than the tray.


amusement A Poka-yoke classic: the go/no-go gauge applied to customers of a play area in a mall.  Look for this type of device anywhere kids are.



tooth brush2






When the forces of commercial self-interest and of dental hygiene combine, how can it not lead to mistake-proofing?  This toothbrush has colored bristles that become clear at the tips of the bristles through use. When it starts to look like the brush on the left, it is time to buy a new toothbrush.  Planned obsolescence at its best.


metric blue

A company called Metric Blue offers metric bolts tinted blue.  Why blue? So that when you have mixed metric and inch-series parts and fasteners it is easier to determine which standard you are working with. Company literature says, “by differentiating the metric fasteners (and tools) through our "blue" coating,  we've eliminated the risk of failure or accidents due to mismatched components.”


toilet paper.

At Boy Scout Camp, some young men get a little carried away dispensing the toilet paper. Perhaps it is their digestive system’s response to the change in diet at the mess hall, or perhaps it is just for fun. These excesses sometimes lead to clogs the plumbing, other times the toilet paper ends up wet on the floor.  One attempt to reduce these occurences is a toilet paper dispenser that only makes one rotation at a time.  In the photo, the upper arrow shows a steel pin that hits the cam, identified by the lower arrow.  This prevents some of the “freewheeling” behavior some scouts may have on their first few occassions away from home.

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