What is my cucumber?

Hi, sounds like a ridge cue which is outdoor. Planted it will send out laterals with 4-6in. cues on them, quite tasty but the skins are sometimes a bit tough.

I was given a ridge cucumber which I have outside.  I did not realise until recently that these like to scramble along the ground and I spent a happy 45 mins doing a Blue Peter and made a rather nice frame for it out of bamboo canes and green netting.  It is climbing up there quite happily and has produced one cucumber, which is about 6" long.  Can anyone tell me how I can tell whether the fruit is ripe enough to pick?  It feels very hard to the squeeze so I don't want to pick too early.  This is the only cue on the plant, but ther have been quite a few flowers.  Maybe it would have been happier sprawling, but there is not the room for it to be unattached from its frame now.