The 40 Watt core was named after its light bulb shape and differential in the forties. You can expect medium flare potential from this core.
Core Type
Symmetric
16 pounds
RG
2.550
Diff
0.040
15 pounds
RG
2.520
Diff
0.041
14 pounds
RG
2.530
Diff
0.034
13 pounds
RG
2.560
Diff
0.030
12 pounds
RG
2.630
Diff
0.025