Pylon questions

Currently outstanding questions about UK electricity pylons and about this site.

Site questions

What is the best way to depict partial approximations? That is, diagrams where part of the drawing is based on industry material and parts of it are based on Street View. The dotted outline form is too easy to mistake for optional components but using a colour implies a highlight and thus a greater level of certainty.
What is the best way to handle depiction of crossarm plans? These are helpful for recognition.
What is the best way to show square-ended crossarms? This too is helpful for recognition.
Should each L6 type be split onto a separate page to ease page complexity? How about the two L3 types?
Is the main series page becoming overloaded with images? Should it be constrained to, say, just line towers and 30° towers?

Some of the tower type designations (e.g. DTU, STX) remain undefined: what do they each mean? Moreover, what is the meaning of DTV 45° (0–5° entry)? What does the 45° indicate if not entry angle? Also, why did National Grid change this to DTU45?
Is it true that “crossarm” originally referred to a pair of arms on the basis that they were a single assembly? (In more recent decades, the arms on each side are completely separate to allow individual replacement and correspondingly appear to be treated as pairs of crossarms.)
Is there any definitive, conclusive information on the “(c)” and “(m)” suffixes, especially with regards to L4(m) versus L6(m)? There seems to be contradiction as to which one denotes nearest metric sizes and which one indicates a redesign, and the exact manner of the redesign.
What is the definition of a panel? This is a portion of a tower but it’s not clear what it means. For L3(c) it denotes a large section of a tower while for Milliken E177 it just seems to denote the points where bracing attaches to the tower corners. One view is that it relates to height extensions.

What is the advantage of using duplex (paired) insulator strings? They are common in countries such as Germany, but not typically used in Britain, with notable exceptions: GPO crossings (for redundancy) and L6 (to share the same insulator sets between twin and quad Zebra towers, with duplex sets for quad Zebra).

~~Why does Britain use shorter earthwire peaks (and thus lower earthwire shade) than say Germany?~~ — It does not: the placement of two side-by-side phases on the lower crossarm on many German towers requires a taller peak to maintain sufficient earthwire shade which, on average, is the broadly the same range of shade angles as the UK.
What are the criteria for requiring an earthwire? For example, most 132 kV steel tower lines have one, but a few lines in Scotland do not. “Trident” wood pole 132 kV lines do not either, just as how 11 and 33 kV do not.

Where does the “PB” designation come from, and was this type solely a Painter Brothers product from design to fabrication? — The official designation is “Painter’s Universal or PU Pole”, also written as “PU pole”, and it is Painter Brothers’ own design. The “PB” name however remains a mystery, in terms of who actually uses it and why.

All known gantries seem to be SFX. What does “X” stand for, and was there also a standard SF tower? Does the X relate to that in DJ/DJX and ST/STX?

Was there ever an imperial L4 pre-dating the metric L4(m)? That is to say, does the “m” indicate that L4 was metric from the start, or does it denote a metric adaptation akin to L6(m)?