Nelson springs:

Main spring is 2.0" long, about 0.48" od, 0.375" id

valve spring is 1.0" long, about 0.36" od, about 0.265" id


valve tube inside diameters:

tube # inside dia. (tube brand measured)
-2 .112" (unknown)
-1 .114" (unknown)
0 .122" (unknown)
1 .134" (unknown)
2 .142" (unknown)
3 .152" (carter)
4 .172" (lapco)
5 .174" (unknown)
6 .189" (lapco)

After talking to Colin (Mr. LAPCO himself), there was actually an agreement between everyone making powertubes as to what ID corresponded to what tube number.  He's long forgotten what those numbers were ("they're buried out in the shop somewhere", he tells me) but says that TASO and Jerry Dobbins (Line SI/ICD) would probably know.  Colin also mentioned that Lapco powertubes marked with a 'P' were to be used with the 'cupped' face cup seals that he had used at one time, and were machined 0.020" shorter from the back end to the back of the hammer stop to account for the different cup seal.  Also mentioned that LAPCO valve seats always had neoprene o-rings, and were always hex shaped.

Talked to Jerry Dobbins on 12Nov2002.  Here's the scoop:
tube #
inside dia.  (Line SI)
Line SI only made those 4 power tube sizes.