I found this web site that had information on plug heat range rating:
http://www.rcuniverse.com/forum/beginners-85/8376353-good-guide-selecting-correct-glow-plug.htmlGeneral Glow Plug Information - Consolidated
By James McCarty, Brian Cooper, and Brian Gardner
OS Glow Plug Information
# 8 Hot Recommended for most current O.S. (and other) 2-stroke engines
Type F Mildly Hot Special long-reach plug recommended exclusively for O.S (and other) 4-stroke engines
Type RE Hot Special long-reach plug designed exclusively for O.S. Wankel rotary engine
A5 Cold Recommended for most current O.S. (and many other) 2-stroke engines particularly for 1/10th & 1/8th scale off-road car engines
A3 Hot Dependable O.S. quality makes A3 the most durable and longest-lasting glow plug available at an economical price
R5 Very Cold Recommended for high-nitro fuel and high r.p.m. engines, particularly 1/8th track racing car engines
ENYA Glow Plug Information
# 3 Hot All Enya engines such as TV & four cycle engines
# 4 Mildly hot All Enya engines, especially those used with 10%or greater nitromethane fuel
# 5 Medium All Enya engines, especially the .40CX, .45CX and high nitro methane fuel
# 6 Cold High compression engines and high niro methane fuel used in racing.
Fox Glow Plug Information
All 1. 5 Volt Plugs are Dry Cell or Ni-Cad All 2 Volt Plugs are Lead Acid Battery
Standard Short Hot 1.5 Volt, Standard Short Hot 2 Volt
Standard Long Hot 1.5 Volt, Standard Long Hot 2 Volt
Gold STD Long Plug Hot 1.5 Volt, RC Short Mildly Hot 2 Volt
Gold RC Long Hot 1.5 Volt, RC Long Mildly Hot 2 Volt
RC Short Mildly Hot 1.5 Volt
RC Long Mildly Hot 1.5 Volt
Miracle Plug Hot 1.5 Volt
Pro 8 Short Cold 1.5 Volt
Pro 8 Long Cold 1.5 Volt
McCoy Glow Plugs with OS Equivalent
MC-8 Medium Hot #8 (thanks for correction, mvbashers.org)
MC-9 Cold A5, R5 (thanks for correction, mvbashers.org)
MC-50 Hot IDLE BAR - LONG
MC-55 Medium Hot A3, #8
MC-59 Hot
Hope I gave proper credits to the original authors.
Best, DennisT