Major diameter - 'Dm'; Overall length - 'Lo'. Sort-of intutive or obvious too by the dimensions given for each term and the decimal equivalents of the metric dimensions given. I would not be surprised if Tom wound his own spring since the combination of dimensions for his spring do not directly convert to anything commercially available - at least in my search.
BC
Pop safety valve
Re: Pop safety valve
"Dm" is the center diameter. Dm + d = spring outside diameter. Or: Ø8mm + Ø1.25mm = Ø9.25mm = Ø0.364in. We chose Ø0.360" since it is very, very close. Sorry for the mistake on "Dm".
BC
BC