Where to obtain tubes for bee hotels.

I have looked on e bay for 'tubes for bee hotels', but tubes results in some sort of neck or head wear.
Some of the larger diameter bamboo may work, but the hollow part only goes a short distance. Not sure yet what length is needed. Need to look at some clips on YT maybe.
Some of the larger diameter bamboo may work, but the hollow part only goes a short distance. Not sure yet what length is needed. Need to look at some clips on YT maybe.
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What sort of diameter are the steredent tubes-about 20mm? I save tubes from effervescent vit C tabs, and put small drill bits in them. Would you say they are about the same diameter?. By the way, would I need to cut the base off of the tubes or leave them?
Can you tell me please what is the the min & max diam bamboo you use . I imagine there is an ideal diam?
Also, thank you for the heads up regarding the Greater spotted woodpecker.
This is a good place to source paper tubes if you want to try that route.