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Dave you are correct it's a stacked ball arrangement but there is no seat beyond the drilled hole in the casting.
TonyWhen seating ball clacks do not use a stainless steel ball ,use a hard steel ball as used in a bearing ( you can get them use ) one hit with small hammer and a brass drift , then bin that ball , now put in the stainless steel one and assemble the valve Opps forgot the hard ball needs to be the same size If you have hit the soft stainless ball it will be deformed and is now useless Stuart