i have a 50l thermopot and got my fb from the home brew builder. it's 392mm diameter which allows for a run of beer line around the perimeter. the beer line makes a nice seal between the fb and the pot. i think there may be some slight variations in the id of the thermopots so you'd need to take your own measurements. the material used was 1.5mm perforated ss sheet and the perforations are, I think, 2mm. the cutting of the sheet was done by laser which resulted in a very neat and accurate finish. I used it for the first time last weekend and it worked really well. overall a very well built product. obviously i can't say how it compares with the other products out there.