The consonant pair ST is very common in English and as such has its own stroke. The ST sound is represented as a vertical downstroke with a hook on the left side of it. Like a mirrored Th stroke.
Straight downstrokes or horizontal strokes followed by an R sound can be written as the downstroke with a small hook on the end. The hook can be on either side of the stroke. The use of the R hook over the R stroke is dependent on context and how well either joins to the rest of the outline. However the hook should tend to be used.
Using the ST stroke and R hook rule combines to create a single stroke for the STR consonant combination.
Straight upstrokes followed by a K sound are always (not optionally) written with a small hook at the end.
