Extending an iron shaft - - which size extenders ???

[Scotland blue]

If the iron shaft is .600 and you want to extend that, would you use a .580 sized extender or is the .600 extender intended for .600 shafts with an allowance in size?

[aerospace_ray]

1 hour ago, Scotland blue said:

If the iron shaft is .600 and you want to extend that, would you use a .580 sized extender or is the .600 extender intended for .600 shafts with an allowance in size?

Are we talking steel shafts or graphite shafts? See Golfworks comment quoted below:

Steel Shafts: " With steel shafts you match the extension size, S56, to the outside butt diameter measurement of the shaft such as a .560" butt diameter. " (Jim Y./Golfworks > https://www.golfworks.com/premium-extension-gauge/p/gw4000g/ )  

Graphite Shafts: " With graphite shafts you have to know the inside diameter measurement at the butt end of the shaft such as the .560" measurement you have with the gauge. Graphite shafts vary a lot more in shaft weights and that effects the wall thickness of the shafts"(Jim Y./Golfworks > https://www.golfworks.com/premium-extension-gauge/p/gw4000g/ ) .