Got two lines of the same brand, one 5wt and one a 6wt. Only problem is I have forgot which one is which as they are both on reels now. Silly question but I have to ask to make sure, but there is no way I will ever know now is there?

Weigh them the heaviest will be the 6.
Cheers

cast them

10/10 .That's how I would do it.Go to the post office and find an unused counter(there's alway's a couple) and stick it on the scales.

Jim

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The Fishermans Friend is the Flirty Fly,Fickle Food for Fleeting Fish.

Most modern kitchen scales weigh light amounts .

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Previously known as molley
and
Don't call me "mate" .

a simple seasaw would let you know but if you cast both I'm sure you could tell any way.

must agree with molley talk to the missus and use the kitchen scales

why not just look at them, 6 belly should be thicker and often longer than a 5.