Why ask diameters, dimensions and lengths?
With the purchase of a new cruising spinnnaker, I decided to replace the jib halyard assigned to it and wound up deciding to replace all the sheets, lines and halyards on my 78h30. Forget the math; just cut off a short length from your current halyard or line -- while leaving it in place; DO NOT remove it before you're ready to replace it -- and hop on down with that swatch to your friendly neighborhood boat supply place, hand it to them and tell them you need -- in my case -- 110' of each one of those...for halyards. They just match the size, run it through the rope-a-matic and, viola! new halyard.Take it back to your boat, securely tape the end of the new halyard to the existing one and use the existing one to "fish" the new into place -- up the mast, through the sheeve and back down to you! Simple!! Took me less than 15 minutes to get the replacements in place and about another hour to put eye-splices in braid. A note on splicing braided line; DON'T think you can learn to do this by reading the manual and paying $50 for the braided line splicing kit of fids and push rods. First, the instructions make NO sense, so find someone who knows how and get them to SHOW you how. Second, I use a stick I marked to measure the different points of entries and exits and I used a looped piece of piano wire to "fish" the various pieces -- covers and cores -- back through one another. Just a couple of quick pointers there.In deference to my learned friends, particularly Mr. Dion, hogwash on ordering the stuff from out-of-town. All the replacements on my boat cost me about $250 and that's pretty reasonable considering I bought almost 600 feet of line. I can't see where there would be appreciable savings justifying the wait for mail-order, but, then again, I guess you could have a rigging shop someplace do all the splices and stuff for you...I just happened to know how to do all that myself. And, oh, yea, I'm a big supporter of the LOCAL folks.