shaft numbers

is a 5.5 shaft a "stiff" shaft? whats the deal on the numbers??

I guess you're talking about the Project X shafts.

The higher the number the stiffer the shaft.

5.0 regular

5.5 stiff

6.0 very stiff

yes. that answers my question, thanks

Here's a shaft-flex comparison chart courtesy of GolfWrx.com. It compares TT/Dynamic Gold, Project X and KBS shaft varieties using Frequency Coefficient Matching (FCM).

The different shaft manufacturers don't have a common flex rating system. This chart compares the three varieties using the FCM ratings used in Project X shafts (5.0, 5.5, etc.)

For example a Dynamic Gold S300 - rated as stiff - has an FCM of 5.8, whereas the PX 6.0 - also rated as stiff - has an FCM of 6.0... So the PX "stiff" is a little stiffer than the DG "stiff." Your 5.5 would be rated as "firm" (between regular and stiff) by PX.

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The chart also contains subscripts on some shaft categories, ss for softstep and hs for hardstep.

• Softstepping: You put a 3i shaft in a 4i, 4i into a 5i, etc. throughout the set. This softens the shaft by about one-third a flex.
• Hardstepping: You put a 4i shaft into a 3 iron, 5i into a 4i, etc., throughout the set. This stiffens the shaft by about one-third a flex.

(Talk to a clubsmith about this; it's a complex process - the stepping also involves shaft length adjustments.)

Got a driver 5.0 flex, asked for a senior or light flex. Got a replacement that shows 5.0 also, sure seems like the same shaft. Anything usually available such as 4.5, 4.0 on a driver?

My clubfitter says 5.5 graphite is roughly equivalent to an "R".....However, he cautioned, "R", "S" "A", etc flexes are subjective and vary by manufacturer.  One manufacturer's  "R"  may be more like "S"  by another, and visa versa.
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Found several references:

http://golfclubbrokers.com/blog/complete-guide-to-project-x-flex-codes/

Also at Taylormade under golf clubs, shafts & accessories but can't get the link to copy, just the main link copies: 

 https://www.taylormadegolfpreowned.com/

http://www.golfshaftreviews.info/understand-golf-shaft-stiffness-ratings/

I have a set of irons with Mizuno graphite shafts (shafts are from Japan)   ....they are labelled Lite-Flex and on the other side of the the label Flex 8...I would like to know what Flex they would be in America....also kick point if possible.

Thanks