Ordering a Lead Screw over the internet 101

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    Typical of a lot of vendors on EBay is to show a nice photo of a screw and nut. The description can read “T8 Lead screw XXXmm length….” That description is incomplete as there is one important specification left out. Unless you are purchasing from a qualified vendor like Ryan that is a part of an engineered assembly or the like, you need to know the Lead of the screw. Lead and pitch are not the same. The typical Lead can be 2, 4, or 8mm. I believe the T8 refers to the mean thread diameter but I can’t find the exact definition. Most lead screws available on the web seem to have 4 starts with a lead of 8mm.

    1. Pitch: The distance between screw grooves. In this case 2mm. Good to know.
    2. Lead: The linear travel the nut travels per one screw revolution. Very important.
    3. Start: The number of complete threads on the screw. Important Typical is 1, 2, or 4.

    Lead in mm = (Start) X (Pitch in mm)

    If you want speed then the longer Lead is what you want. If you high precision the lower Lead is right. It’s all a compromise. I’m not recommending what lead to use, that’s up to your need. I’m just trying to help people to order and get what they need the first time. Been there done that.

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