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Last month I wrote about a tool called the Size Catcher I found while browsing one of my local hardware stores. Since then I’ve picked one up for $5 at Menards and have played with it for a few weeks. Here are my impressions of the tool:


I find the snap ring annoying since I hate having tools on my key ring — just what you need, keys dangling from the tool you’re trying to use — eventually I’ll get around to removing it. I have been carrying the tool in my pocket for the last few weeks and have forgotten it was there several times. I’ll take it out of my pocket every time I see a nut or bolt and play the see-if-I-can-guess-what-size-it-is game before I measure it.

You can see in the above picture that on the inside of the tool there are raised ovals. What this means is that the numbers are stamped, not etched, into the metal. It’s obviously cheaper to stamp the numbers rather than etch them, and for this product it doesn’t seem to affect its performance.

A commenter in the first post wondered about the shape of the jaws. I think the shape is intentional. The fastener rests against the back of the jaws making it easier to align the tool, while the rounded jaw tips only contact the nut at a single point. Due to the way the tool opens and closes, flat jaws wouldn’t stay parallel and pointed jaws might get damaged, making the tool inaccurate.

The button/indicator has a couple of raised lines for grip. Both sides of the indicator are riveted together somewhat loosely, so that no matter the position of the jaws it can move back and forth about an 1/8″.

Because of this play, using the Size Catcher takes some getting used to. It can be hard to distinguish between two marks, especially on the more closely-spaced metric side. What you need to remember is that you have to read the position of the indicator when it’s closest to the jaws. This is because as you push up against the indicator it closes the jaw against the fastener. The slack when you relax you finger on the indicator is the distance the button has to travel before it makes the jaws start to open.


Of course what you really want to know is, if I measure a fastener with this tool, am I going to get the right size? If you go grab a tool based on what the Size Catcher reads and find out it’s not the right size, it’s just a waste of money. To test the accuracy, I set my calipers to a specific size and read the caliper’s internal jaws with the size catcher. Here are the results:

Caliper -> Size Catcher

  • 8mm -> 8mm
  • 9mm -> 9mm
  • 10mm -> 10mm
  • 11mm -> 11mm
  • 12mm -> 12mm
  • 13mm -> 13mm
  • 14mm -> 14mm
  • 15mm -> 15mm
  • 16mm -> 16mm
  • 17mm -> 17mm
  • 18mm -> 18mm
  • 19mm -> 19mm
  • 20mm -> 20mm
  • 21mm -> 21mm
  • 22mm -> 22mm
  • 23mm -> 23mm
  • 24mm -> 24mm
  • 25mm -> 25mm

Caliper -> Size Catcher

  • 5/16″ -> 5/16″
  • 11/32″ -> 11/32″
  • 3/8″ -> 3/8″
  • 7/16 -> 7/16″
  • 1/2″ -> 1/2″
  • 9/16″ -> 9/16″
  • 5/8″ -> 5/8″
  • 11/16″ -> 11/16″
  • 3/4″ -> 3/4″
  • 13/16″ -> 13/16″
  • 7/8″ -> 7/8″
  • 1″ -> 1″

Not one of the readings was ambiguous; in fact most of the time the indicator was dead on the line. I think my data shows without a doubt that when you use the tool correctly, at least the one I own, you get the correct reading.

Another thing you’ll find using this tool is the right wrench for the job isn’t necessarily the one you think it should be. For example, you’d think that the best wrench to use on a 3/8″ nut would be 9/16″, but I found some 3/8″ nuts in my shop that actually measured much closer to 14mm. In the above photo, you can see the gap between the nut and the wrench is actually larger for the 9/16″ than the 14mm. The difference is probably too small to cause any damage by using the larger wrench, but it is interesting.


In short, the Size Catcher is small and lightweight enough to lose in your pocket, and it does what it claims to accurately. If you can find it cheap, I recommend it. The problem comes when you end up paying more than $10 because either online retailers jack up the price or you have to pay exorbitant shipping charges.

Size Catcher [Wilmar] (search for size catcher)
Street Pricing [Google Products]
Via Amazon

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10 Responses to Hands-On: The Size Catcher

  1. Ben Granucci says:

    If only they made one that was for smaller items and displayed screw sizes (#6, #8 etc) I would be all over this. 8mm and 5/16″ is often larger than the tools I am using. Heck, the first set of wrenches I bought for work were ignition wrenches. That’s the scale I am working in much of the time.

  2. A.Crush says:

    Possibly one of the best uses of the tool is as you state, playing the guessing game, and hopefully learning to correctly guess the size of a fastener merely by sight. The tool will still have use once you learn, since there are plenty of times you can’t see a fastener that well but need to know a size rather than bring over a lot of extra tools.

    I don’t know why you’d use a 9/16″ wrench on a 3/8″ fastener though, or even a 14mm, unless you don’t have a 3/8″ wrench.

    $10 seems like a heck of a lot for this, since $10 can buy you an entire (cheap) SAE & Metric wrench set. Seems more like something you’d see at point-of-sale displays for 99 cents or maybe a few bucks.

  3. Toddi says:

    $4.99 at Menards seemed right, props to prior midwest postee for sending me there.

  4. Geoff says:

    Regarding the 9/16″ wrench on a 3/8″ nut, don’t you mean a 1/2″ nut? 3/8″ is 3/16″ smaller than 9/16″ but 1/2″ is only 1/16″ smaller. I’m with A.Crush, I don’t understand the rationale behind using a different sized wrench…

  5. browndog77 says:

    @ crush & geoff
    A 3/8″ nut refers to the thread size of the bolt or stud. The standard hex size for that nut is 9/16.

  6. jesse says:

    Only $5.45 at The Tool Warehouse: http://www.thetoolwarehouse.net/p-9454-performance-tool-wilmar-w9162.aspx, plus free shipping on orders over $75.

  7. Tybee508 says:

    Going to Menards today to see if I can find one at the $4.99 price. This will be a great stocking stuffer for my husband. Thanks!

  8. arcticcatmatt says:

    Thanks for posting this. I snagged 5 for stocking stuffers online 🙂

  9. Kyle says:

    Thats awesome! What a time saver!

  10. codopa says:

    I picked up one of these at tractor supply company (TSC) about a year and a half ago for $2.99. like you, I found it just browsing around the tool aisles. I found it to be accurate and easy to use, even though I’ve probably only used it a dozen times or so.

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