Some of the cork logs are enormous! Really long - reptile centres sell them or Amazon. I get the one that Rodipet sells because it's the right length for a hamster cage. Not cheap but adds well to enrichment and doubles up as a ramp.
I had the medium and the large but the large works best as it's the right height for a ramp. Our robo used to love sitting inside it scratching his nails on the inside of it! It might seem unnecessarily large for a hamster tunnel but it's more than a tunnel as provides overhead cover instead of hanging items from the roof.
https://www.rodipet.co.uk/accessorie...-diameter.html