prop shaft flange bolt size

Aug 24, 2020
Hunter 28.5 Portsmouth
Does anyone know what the correct size socket/wrench for the prop shaft flange for my 86 28.5 is? 5/8 is too small, 11/16 is too big, 16mm is too small, 17mm is too big. Feeling a little frustrated here. Thanks.
Oct 10, 2019
Signet 20 107 Ithaca
I know nothing about the "correct" size, but whichever "too large" socket is tightest should be the right one, metric vs imperial is irrelevant. But if the too large sockets spin, and the too small sockets don't fit, there are no other options In a socket.
Dec 14, 2003
Hunter 34 Lake of Two Mountains, QC, Can
A few options might work:
  • You could try to find a socket calibrated in 64th. Between 5/8 and 11/16 you might be lucky and find a 41, 42, or 43/64 that will fit. Never seen one but who knows in a specialty shop ?
  • Don't know of any metric sizes between 16 & 17 mm !
  • You might find open-end wrenches in those SAE sizes and use that.
  • Another resort but one I don't like is Vise-Grip pliers.
  • If I had this problem however, I would try to sand / clean the sides of the nut until I could fit the smaller socket.
  • And if that did not work, I would use a cut-off wheel on my grinder and cut the nut off the bolts, replacing bolts and nuts with new ones afterwards.
Good luck
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Aug 24, 2020
Hunter 28.5 Portsmouth
So I did a little searching around and it turns out there is a specialty size between 5/8 and 11/16, a 21/32, I don't know if it's the right one but for $4 it's worth a shot. If not, I have a set of universal sockets that may work. If all else fails then cutting may be the only option, the bolt heads are rusty but they don't look compromised. Guess well see...
Kobalt Universal 9-Piece Standard (SAE) 3/8-in Drive Spline Set Shallow Socket Set in the Sockets & Socket Sets department at
Feb 26, 2009
Oday 30 Anchor Yacht Club, Bristol PA
Aug 24, 2020
Hunter 28.5 Portsmouth
These are made for the problem.
we use them on my Ford ranger that had recessed 12 point head bolts. You can bang them on with a hammer they have very sharp reverse teeth and they cross over between metric and standard sizes

but ... you should just cut them off anyhow. Because you're going to replace them.... right?
I have a set of those too, they are definitely getting replaced.