I'm not sure where you got the sizes from but one that I just did a quick search for quoted the following sizes. 264mm X 164mm X 80mm.
Some may quote the size of the inside of the basket but say the inside of the tank, the inside dimensions of the basket is the best dimension to have as that really tells you what you can fit in to the M/C. You can use these M/Cs with out the basket but then you have to start getting your hands in to retrieve the parts Etc.
Adrian, mentions how do you know it's clean and it's not all down to all of the prep. work before putting in the cleaner? Maybe some of it just down to trust in that these things are used in the medical profession and jewellery trades to clean things. It's a bit like putting a 'clean' kid in the bath you know it's going to be cleaner when it comes out (but can you see it's any cleaner?)
I think that this may show what can happen using an U/S cleaner, new fluid on the left used fluid on the right,
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The one on the right has been used a few times, that is not the grot off one build. It will settle down and all of the big bits will go to the bottom but the fluid will never be as clean as the one on the left as some of the muck (oil, grease Etc.) will be in suspension. To make sure that is removed you just use some fresh warm water in the U/S cleaner.
This was after a set of parts had been grit blasted and had a good wash using Cilit Bang using hot water and then a run in the U/S cleaner, I thought the parts were clean before the U/S cleaner. This is what was left in the cleaning tank!
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OzzyO.