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hex wrench size for Big Mouth Air Vent BJ-3BM?

rhodebumprhodebump Member Posts: 118

I feel exasperated. I have a set of large hex wrenches (3/8 through 3/4 inch) but nothing fits
1/2 too small
5/8 too big
9/16 too small

I am about to grind a chisel to install, but I wish I could just have the order the proper tool. Is it metric? Is my hex set defective?

I appreciate pointing out my mistake.



  • FredFred Member Posts: 8,423
    It's a 5/8" Hex
    rhodebumpSTEAM DOCTOR
  • rhodebumprhodebump Member Posts: 118
    Fred said:

    It's a 5/8" Hex

    I will try it again, and verify the size on my hex.
  • JUGHNEJUGHNE Member Posts: 6,971
    A little grinding or filing on the 5/8" hex or chisel.
    Or a bolt with 5/8" head with 2 nuts jam locked to wrench on.
  • Hap_HazzardHap_Hazzard Member Posts: 2,263
    edited January 8
    15 mm is right in between 5/8" and 9/16", but I can't see Barnes and Jones using metric sizes.
    Just another DIYer | King of Prussia, PA

    1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24
  • SailahSailah Member Posts: 824
    You can just asemble it and crank it in to bury the threads. Loosen the union nut and readjust
    Peter Owens
  • LardLard Member Posts: 58
    > @JUGHNE said:
    > A little grinding or filing on the 5/8" hex or chisel.
    > Or a bolt with 5/8" head with 2 nuts jam locked to wrench on.

    This is the method I used, but a little more “Ohio Hillbilly”. I used a junk spark plug with the insulator removed inserted “engine side up”—the large diameter and long threads afforded a nice place to get a good bite with a small pipe wrench. It worked! Said spark plug is now welded to a cracked chinesium 15mm socket I had laying around, creating a dedicated 1/2” drive “Big Mouth socket”

    5/8”/16mm is an oddball Allen wrench size, but certainly is not an oddball hex bolt size!
  • rhodebumprhodebump Member Posts: 118
    All, I found out that the hex set that I bought on amazon was junk. People verified with digital calipers that the 5/8 hex was off. I bought a 5/8 hex from a different vendor and it fit perfect. I think there are some tools that are even worse...than harbor freight (audible gasp from the crowd here) ;)

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