I’ve noticed there is quite a problem with people determining the type of lead screw they have. They’ll think they have a T8x2, order a replacement nut or anti-backlash nut or Delrin nut and it won’t fit their screw. Usually this leads to a message accusing me of sending the wrong item. The vast majority of the time, they just got the lead wrong.
The most popular size of Lead Screw used on 3D Printers is the T8. The 8 stands for 8mm in diameter. But it’s the second number that you have to pay attention to when buying lead screw nuts,. The number following the X is the Lead or distance the nut travels with one full rotation of the screw. There are three popular travel distances for Lead Screws, the most popular being T8x8 or in other words 8mm diameter screw and the nut travels 8mm with one full rotation of the screw. The second most popular is T8x2. With this screw the nut only travels 2mm in one full rotation. The third popular type is the T8x4, where the nut travels 4mm in one rotation. The most popular as I said is the T8x8, it was for a long time the cheapest of the screws to produce it is also the worst of the screw sizes due to the large travel distance and the drop in quality that entails. Lately though as demand rises the pricing curve has flattened and you can get all three types for roughly the same price.
How to Determine What the Travel Distance Or Lead of Your Lead Screw Is.
Take the nut your lead screw came with and mount it. Place a piece of tape on the screw and the nut. Mark both pieces of tape in the same place so the marks align. Rotate the screw one rotation, moving the nut away from the tape. When the marks align again, measure the distance the nut traveled from the tape. If it traveled 2mm then you have a T8x2, 4mm you have a T8x4 and 8mm you have a T8x8.
You can try to judge what you have by looking for visual distinctions between the types of screws but many people who are inexperienced usually are wrong. The rotating tape method is the surest and easiest way to figure out what type of lead screw nut you need to get.