Thread pitches

Discussion in 'Engineers' Talk' started by Guy, Jan 18, 2004.

  1. Guy

    Guy Member

    Not being an engineer, I have a query regarding the pitch of a thread.
    Now and again I need to tap a thread into some steel, but find differering pitches to choose
    M5 x 0.8 M5 0.9 What is the difference between these two?
    If I want to tap an 8mm thread, and go to buy a tap of 8mm. Will I be asked what pitch I require?
    So, in other words, I have an 8mm bolt, and want an 8mm tap to I need to know the pitch of my bolt before I buy a tap?

    I appologise for my vague description but as I confess, I am not an engineer, but would be grateful for any help.

  2. Dewy

    Dewy New Member

    I just read your 2 posts & then looked at the tap & die set in SFX. Presumably the M5 0.9 is the course thread & the M8 0.8 is the fine thread. Many screw threads have both course & fine threads but are usually shown to be. i.e. UNC & UNF. Each has different uses. I hope this answers your question.
  3. Markybob

    Markybob New Member

    When specifying metric threads, ie M8, this will be standard metric coarse. So all nuts and bolts sold via this site will be of the coarse variety. So a standard M8 tap will have a pitch of 1.25mm, this being said you can also procure metric fine, (M8 is 1.0mm pitch) slightly more specialised and more often than not only sullied by specific engineering tool suppliers.

    If you have found M5x0.9 it is a misprint or mistake, ISO M5 standard is 0.8mm pitch

    UNF and UNC are generally not very common now, still found on american kit though.

    Hope this isn't to wordy, get yourself a zeus table (bible)
  4. Dewy

    Dewy New Member

    I couldn't find my zeus book when i saw the post so had to answer from memory.
    Those pitches 0.8 & 0.9 are definitely shown on the SFX tap & die set for M8.
  5. Markybob

    Markybob New Member

    I've just had a look, the set has the standard stuff and lots that I dont think you would have a use for unless you where creating your own threads. I suppose it all depends on what you want the set for, if you are just making stuff you want to screw together you will be using standard screws, I would just by the taps you require as previously mentioned


  6. Rebel

    Rebel New Member

    Markyboy is right - you need The Bible, but don't be confused as it is sold as 'Zeus Data Sheets'. They contain a wealth of conversions and the sort of info. you are after and fit nicely into your shirt pocket!
  7. Markybob

    Markybob New Member

    Could be is that the set is aimed at the modellers market using them small little lathes in their sheds

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