Chain ring specifications

[vet racer]

I posted a question the other day re buying some dura ace chainrings, thanks to those who replied.
I have a couple more questions if anyone can help me please.
My chainrings are 7900 series. On my 39 tooth ring the following is printed " SG-X 10s 39-B GH".
When I look at an online (British)site the 7900 series ring has exactly the same except the GH is relaced by HD. Does that mean anything? Are they different in any way? Will this one be okay for me to buy?

Also, on the same site, the big chain ring lists as part of the specifications, BCD 130. Can someone tell me what that means please.
Sorry to be thick, just really don't want to buy the wrong type and have the hassle of returning them.
Thanks in advance.

[twizzle]

Bolt Centre Diameter.


Sent from my iThingy...

[twizzle]

... or - if you were to draw a circle with a diameter of 130mm, the centre of each bolt would line up on the circumference. The other common size is 110mm used for compact cranks.


Sent from my iThingy...

[jcjordan]

The GB and HB are series marks to indicate batch production runs

[scirocco]

My chainrings are 7900 series.

Are you quite sure about that? In the other thread you said your bike was 2006. 7900 DA didn't come out until 2008. So unless the cranks have been upgraded they will be 7800, not 7900.