[Researcher]

The original Flues SBT had two extensions with wedge bolting --

Flues SBT early bolting.jpg

First Style No. 4E Flues SBT.jpg

Pretty quickly A.P. Curtis changed the bolting to a Greener-style cross-bolt --

Flues SBT early Curtis bolting.jpg

a bit later the Curtis bolting was modified a bit --

Flues SBT second style Curtis bolting.jpg

All this in a barely seven-year production run