High tension spring used on pinball machine ball shooter assemblies. .038 inch wire diameter.
It's a good idea to replace the outer barrel shaped spring (No.10-149) at the same time as this one.
Reference:
Gottlieb: 26028
Jersey Jack Pinball (JJP): 13-007007-07
Jersey Jack Pinball (JJP): 13-7007-07
Stern: 266-5001-07 orange
Williams: 10-148-3