FWIW, that masthead casting looks very very much like the one on my much much older M17 #38 from 1974. The one exception may be the base of it, to match your mast extrusion. I am pretty sure mine is more oval, less round. I'm not at home right now so can't run out and measure. But could later next week. My halyards are all line. 5/16" I am pretty sure, but a relatively "skinny" 5/16 rather than a "fat" one. Line sizes in inches or mm are 'nominal' and vary in practice for a bunch 'o reasons. Here's a thorough video, the first few minutes explains the basics of why lines labeled the same size are different actual sizes: https://www.youtube.com/watch?v=6lgYxFMR3-0 Anyhow I have the same two sheaves per halyard and the thin separator piece between. I don't know if 1974 OEM for M17 was all line, or wire/line - Jerry? Dave S.? In any case my sheaves would take a bigger diameter material thru them than how yours look. Yours have much fatter flanges and smaller grooves (for wire, obviously). Mine have bigger grooves and thin flanges. If our mastheads are the same casting, I can verify there is room in the setup for nominal 5/16" line for the halyards, if you could find sheaves with a wider groove and of the same diameter. And, 5/16" is bigger than necessary for the halyards, 1/4" would probably be fine. Especially if you used spectra or other low-stretch high-tensile. Just that the thinner the line the harder it is to get a good grip for pulling heavy tension. Can post pics of mine but not until later next week if that is still helpful by then. cheers, John On 11/17/22 20:51, Kevin Brackneyesggbf* wrote:

I’d like to convert my halyard from line/wire to all line, but I can’t figure out who made the mast? The dimensions don’t seem to fit any of the Dwyer masts. I’m assuming I need to purchase a new masthead as the existing has 4 sheaves for the wire and there doesn’t seem to be sufficient room for larger sheaves for the line. I’m attaching a picture with dimensions. Thanks, Kevin s/v Jumping Jack Flash #615

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