I'm trying to look for some Allen screws for a friend to help him out, but am unable to figure out the correct size of the screws and nuts he lost (see image, marked in red).. I'm not really familiar with the sizing of it, but do know that the hole has a size of 6mm and the Allen wrench diameter is 4mm. Any help is really appreciated!

The Manual of the screws and sizing..

cage seed guards, consists out of 8 screws and nuts


All the units are in English

These are English, Imperial, or more technically ANSI (A for American) fasteners. They are not metric.

The holes that are slightly large of 6mm are actually for 1/4" bolts. As they say, the bolts are 1-1/4" long. Typically this will be 1/4-20 unless there is an extraordinary need for strength. Since they are bolt-nut pairs, you may be able to substitute 6mm, but the 1-1/4" length will still be essential. " means inch, by the way.

For the 5/16 and 3/8, that figure is the length. Most likely that is a #10 or possibly #12 screw. The smaller screws are most likely #6 or #8.

  • If you see threads precut in the holes, they are machine screws and the matchup is critical, you cannot substitute metric fasteners. Keep in mind machine screws come in different thread pitch: coarse (NC) and fine (NF). These two are standards, and everyone follows them, unlike metric lol!
  • If you do not see threads precut in the holes, then get a micrometer and measure the precise diameter of the receptive (rearmost) hole. Then ask US companies what sheet metal screw is best for that.
  • Thank you for all the help! The holes seem to be like simple holes, there's no thread precut, unlike all the other holes. If I understand correctly, I'll then have to find replacement screws for the 1-1/4" screws that would fit those holes? How would I measure the length of the screw to mm? I did a conversion and it seems to be a pretty long screw, which made me doubt in the beginning. I'm from the Netherlands and not really familiar with inches.. Thanks again for your help, I really appreciate it!
    – Morgana
    Feb 11 '19 at 18:06
  • @Morgana I would find a good hardware store that stocks English fasteners. They may even be cheaper than metric. In America even the shabby hardware stores stock both. There are a lot of English machines in Europe, much of them American. Feb 11 '19 at 18:18

Let me Google that for you...

m6 bolt dimensions

The first number in a metric bolt specification refers to the bolt's nominal outer diameter. For example, a bolt specified as "M6-1.0 x 30" fits a 6.0-mm diameter hole.


  • Thanks a lot!! Do you also happen to know what the 5/16" stands for in the screw sizing? Is it the diameter or size of the thread? I'm trying to figure out which one of the screws I have to search for in the manual..
    – Morgana
    Feb 11 '19 at 14:59
  • Same thing, but 5/16 is in inches (not metric). It'll fit a 5/16" hole, but snugly.
    – isherwood
    Feb 11 '19 at 15:01

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