Quote; I will hopefully be moving them into growbags soon and was wondering how big they should get before I do this.

Where do you plan on putting your growbags? indoors or out?

I don't know where you are but I would say the only place suitable at the moment in the UK is in a heated greenhouse.

Regarding size; What type of container are they in now as this will dictate when to plant them out.

That is they don't want to become rootbound in a pot.

Quote;Also when do I pinch out the growing tip and can someone briefly tell me what this is exactly.

Pinch out the growing tip after the fifth/sixth pair of leaves this will encourage the formation of sideshoots.

Stop each lateral (fruit-bearing growths) at the second leaf joint.

Remove tendrils and pollen-bearing male flowers to prevent bitter tasting fruit as they appear.

This link will offer some further information.

http://www.thegardenersalmanac.co.uk/Data/Cucumber/Cucumber.htm

The plants are currently in 4" pots and I can see the roots at the bottom of the pots. I was intending on putting them in growbags outside, but the weather is horrible at the moment. I'm in the South East and it's a bit chilly and raining a lot at the moment. Maybe I should keep them indoors for longer?