We once had a guest speak at a union/management committee day, he was representative from the ITI (body that governs all SMWIA apprenticeship programs). ...Anyway, he was retiring from the ITI and was moving from CA to TN and was having a house built. On one of his final trips to check on construction, he noticed that the HVAC constractor had used all srare throat/ radius heel 90's. He made the take them out and replace them with full (1-1/2X) radius 90's where they would fit and sqaur with vanes where they did not.
I have made sq throat/radius heel for people that have walked into my shop looking for duct, but have never made that fitting for one of my jobs.
Just like a point to point (no miter) offset, if you measure the distance from the inside of a square throat to the mid point of the radius heel of a sq/rad 90, its got to choked down by at leats 10%-15% I would think.
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