I do old window renovation etc. Typical Victorian or Edwardian sashes or casements have rebates about 18mm x 5mm. This is much smaller than modern windows which are anything from 18mm x 8mm upwards.
18x5 is perfectly OK if you cut the glass accurately enough but there is no room for sprigs except as temporary holding. But its better without them - sprigs create problems. For a neat job there should be a clear line of sight over the 2 arrises of the rebate, through the glass. i.e. putty face and 2 faces of rebate make perfect triangle. More stuff here
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