Nylon slides
I have never heard of external nylon slides, either. If your metal slides are binding, it might just be a symptom of another problem. Some areas you might want to look at before speniding time and money and never really solving the problem - Are the slides seized onto the luff properly or are they loose? Are the slides bent or malformed in any way? Is the mast straight athwartship or is it snaked due to improper tension on the shrouds? Are they the right size? If you have full battens, are they secured in batten cars and, if not, is there a slide at the immediate top and bottom of the batten? Is your main halyard, boom vang totally loose as the main goes up? I occasionally put some dish detergent on my slides before I run my main up. It makes a great lubricant and helps to keep the track clean. Hope some of this helps.RolandS/V Fraulein II