Difference Between Metric and Standard Bolt sizes

August 7, 2019

When it comes time to start shopping for your next order of bolts, you are going to need to know exactly what you are looking for. At Ebolts Online Store, we pride ourselves on offering you not only great products but important information, as well. Today, we are going to be discussing the primary differences between standard and metric bolt sizes. We'll be talking about the difference between the two systems as well as what you should pay attention to when you make your next order.

Metric vs. Standard Bolt Sizes

When we discuss the core differences between metric and standard bolts, we are essentially discussing two different systems defined around the same subject. The international marketplace is typically going to be filled with parts that are graded by the metric system. The metric system relies on metric units, such as millimeters. When we discuss standard bolt sizes, we are more often talking about American Standards. America uses measurements that revolve around units such as inches. With that being said, there is a little more going on underneath the surface if you care to look. Let's go ahead and examine some key differences, below.

1) Understanding American National Standards

When delving into the differences between metric and standard sizes, you'll have to refer to the ANSI standard. ANSI stands for American National Standards Institute. This group has put together standards for both metric and standard sizes. You'll find that standard can be translated to metric with the addition of a single M at the end of the name. For example, standard hexagon bolts will be listed as B18.3.5. Metric hexagon bolts will be listed as 18.3.5M. Within those standards, you'll find even more information. The B18.3.5 hexagon bolt has a diameter ranging between 1/4 and 3/4 of an inch. Conversely, the metric version of the same name will range from 3 mm to 10 mm.

2) Digging Into Fastener Size Designations

When we talk about the concept of thread pitch, we are describing the space in between bolt threads. Metric fastener sizes will start with an M or MJ followed by the nominal diameter as well as the thread pitch. American standard bolt sizes are defined within the inch system. For example, a Metric fastener could be labelled as M10 x 1.5 while defining a nominal diameter of 10 mm and a thread pitch of 1.5 mm. Standard bolts would be listed as A 1/2 - 24, with that defining how many threads per half of an inch.

When it comes time to order your bolts, make sure you are getting what you need. Here at Ebolts Online Store, we can help you find the standard or metric bolts, nuts, screws and fastners that you require.

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