Answer: Cucumbers are usually self supporting on the vine when trellised (especially if you pick them often and do not let them get too big and old).
If you're concerned about their weight you can provide plenty of support. Gardeners have
fashioned all types of supports from sections of hosiery for smaller fruit such as small squash and cantaloupes, on up to slings made of torn sheets or netting for watermelons and pumpkins. Tie the support to the trellis when the fruit is the size of a baseball or softball and as the fruit grows it will provide adequate support. It is best to use materials that do not stretch too much or the growing fruit will cause the support too sag and not do its job. Check the supports periodically to make sure they are working right.
You may find this article, "Trellising Vine Crops",
http://www.garden.org/qanda/nga/articledetails.taf?id=642&kw... helpful. Thanks for writing!
Q&A Library Searching Tips