Think you've found the perfect shift knob to dress up your gear shifter? Before you lay down your hard-earned money for it there's one thing you should check- the thread size and pitch of your gearshift lever. Though a shifter knob made for your specific auto make and model might not need to be researched, when you're looking at performance and custom shift knobs verifying the thread size or thread pitch of your ride's shifter will save you a lot of headache and hassle. Before you determine the thread size or pitch of your gear shifter you first need to find out how it is measured, in English or metric. One easy rule of thumb is to go by whether your car, truck or SUV is domestic or foreign made. American automakers tend to use English measurements, especially on older models. However, since domestic automakers are teaming up with European and Asian manufacturers just looking at the name badge bearing an American company name doesn't mean the vehicle was made in the US or measured in English. Chances are if the country of origin isn't the US, Canada or Mexico, all pieces, including your gear shifter, will be metric.
Okay, so you've determined whether your gear shifter thread size is measured English or metric. But there's a lot more difference between English and metric thread sizes than the obvious use of inches versus millimeters, though that will help you pick the right size of shift knob. English thread size is measured by the diameter of the outer male thread (thread diameter) and the threads per inch of a threaded area, or TPI. When trying to find your thread diameter, simply take a caliper and pinch down to the outer thread of your gear shifter. That reading in inches is your thread diameter. You can also use a ruler for this by holding it across the middle of your gear shifter and estimating what the distance across the end of it is, from outer thread to outer thread. While a ruler will work in a pinch, it won't be as accurate as a caliper. Once you've found the thread diameter you need to find the TPI. To do find the TPI of your gear shifter, simply count the number of ridges in one inch of the threaded area. The number of ridges you count is the TPI! For example of how to read an English shift knob thread size, let's say you were looking at a custom shift knob for your Jeep. If your thread diameter was 3/8 of an inch and you counted 24 ridges in one inch of the threaded area you'd want the Jeep shift knob with a 3/8"x24 thread size. It's as simple as that. Metric thread sizes, on the other hand, aren't quite as simple and use a different method. Like English thread sizes, you still need to measure the thread diameter but in millimeters instead of inches. However, instead of finding the TPI or even the threads per millimeter or centimeter, you measure how many millimeters the shift knob will advance in one complete turn to determine the thread pitch. As you can tell, this is a little more complicated than measuring thread peaks in a given area, though with a caliper or ruler you can get a close estimate. One method you could use is when removing you current shifter knob, use a felt marker or pencil to mark a dot or line where the bottom of the shift knob sits on the gear stick. Then, after one complete turn, make another mark where the bottom of the shift knob now sits and measure the distance between dots. Another method would be to find the beginning of the threading on your gear shifter and use a caliper or ruler to measure the distance from the thread beginning to the first ridge above it. While this will give you a close estimate, if you want an exact measurement there are tools you can buy to help you find it. Once you've found the outer thread diameter and the thread pitch you can determine which metric sized shift knobs will fit your gear shifter. Let's imagine you were looking at a billet skull shift knob and your gear stick's thread diameter was 10 millimeters and you found with one complete turn the shift knob would move 1.25 millimeters. Then the skull shift knob you'd want would have a metric thread size of 10mmx1.25! Occasionally you might come across a shift knob and find the only one thread dimension listed, let's use 12mm for example. Chances are the shift knob you're looking at features a self-tapping sleeve and all you need to know is the thread diameter. In this example, if your gear shifter's thread diameter was also 12mm, you'd have the right size shift knob for your ride! In any situation where only one measurement is listed you can count on it being the outer thread diameter. One thing to remember is because of the difference between determining English thread sizes and metric thread sizes you will very rarely be able to fit a metric threaded shift knob to an English sized gear shift lever and vice verse. Just as you can't fit a metric bolt into a standard hole, you can't fit a metric shift knob onto a shift stick that it isn't threaded for. Because they're easy to install and can add a cool performance aesthetic to your interior shift knobs are one of the most popular interior accessories around. They're perfect for not only making shifting seem more like an adventure but also for helping you personalize and customize your ride. With the help of this guide, hopefully you won't have any trouble finding the perfect shift knob for your car, truck or SUV- whether perfect means style or size! Looking for a sweet custom shift knob? Check out our selection! From polished billet aluminum to carbon fiber, we're bound to have a shift knob that's perfect for your car, truck or SUV!