Is It Standard Or Metric
MYLES CLIFTON
PERRYVILLE, MISSOURI
One common frustration that can come with repairs on the farm is dealing with the difference in metric fasteners and SAE or imperial fasteners. While you may know how to identify the differences between them, not everyone may. Of corse depending on the manufacturer of the equipment sizes and types of fasteners can vary. If you’ve been around some of the older, or even up to pre-1990’s equipment, you know your SAE wrenches well. But production and engineering has changed over the years and manufacturers have become much more global you eventually had to invest in metric tools as well.
We’ve all had times that we’ve tried to work on something and go though more than a few wrenches or sockets until we’ve found the right tool. The common question, “Is it standard or metric?”. Depending on your experience on turning wrenches you may know the difference. But this week’s article is to help those who may not know the difference.
If you’ve paid attention when you’ve taken apart older equipment you’ve probably noticed the markings on head of a bolt or on the edge of a nut. You may know that it refers to the grade of the fastener. But it's also a quick and easy way to identify whether the fastener is metric or SAE. Knowing the difference in markings can easily save you a trip or two to the tool box drawer. Now, we have to remember than not all fasteners, especially smaller, lower grade screws aren’t as easily identified. But for right now we’ll stick to our more common markings.
Believe it or not SAE does not actually mean standard. SAE once stood for the organization know as the Society of Automotive Engineers. An American based group, formed in the very early 1900’s, that’s basically responsible for the development of the “fractional” sizes of tools and hardware we still use today. But also not to be confused as Imperial, while being somewhat related, it is the British Imperial system which has some differences from the SAE system.
Metric nuts are somewhat similar to the SAE markings except for metric nut fasteners typically have a dot to mark them rather than a line, again you have to note the placement of the dots to determine the grade. Being able to identify the difference in metric bolts from SAE bolts its a bit easier than the nuts. Metric grades are marked with numbers, 5.8, 8.8, 10.9, 12.9 and actually sometimes even a 4.8. This makes it easy to identify that this particular fastener is in fact metric, requiring a metric tool.
Another common misconception is the difference in grades. Not all grades are equal. Metric 4.8 and 5.8 are typically equal to an unmarked SAE fastener being lower grades. A metric 8.8 is equal to a SAE grade 5 faster. A metric 10.9 is equal to a grade 8 fastener. Then of corse we get into our much stronger and higher grade bolts. A metric 12.9 and SAE grade 9 (not pictured), are not always as common but are among the highest strength grade fasteners you’ll see around the farm.
Then of corse another big difference is the thread pitch. Again there is difference between metric and SAE, although this is not always as easily identified with just the eye. A great way to tell a difference in thread pitch is by picking up a thread pitch gauge set. Typically, available in separate metic and SAE sets. It can be a great way to know what you’re working with. It’s also a great way to ensure you are able to get a proper replacement for the fastener if needed. But, can also be handy should you need to fix a damaged thread with a tap and die, thread chaser or thread file.
A good habit to do, especially, for a new to you piece of equipment is to become familiar with the types of fasteners found on that particular piece of equipment. Most manufacturers tend to stick to certain sizes of fasteners that they like to use on everything. For example, you can dismantle majority of almost any John Deere made in the last 20 years with a 10, 13, 15, 18, 24, 30, and 32 millimeter wrench or socket. This is why is also a good idea of know the difference in types of bolt and nuts to ensure you can replace a damaged fastener with the same type. While the diameter, thread pitch, and grade may be the same that doesn’t mean the head of the bolt will be the same size. But we can save that for another article.
In the mean time, if you’re curious about the likes of tools such are thread pitch gauges, thread files or even bolt gauges, contact Clifton Tool & Supply LLC, located in Perryville, MO. Call (573)517-1242 or check us out on Facebook at Clifton Tool & Supply. Clifton Tool & Supply is here to help the farmer. ∆