I'll side with Jamal on this one. As far as i know:
The EJ251 and the EJ253 use by default the 11044AA633. Single layered steel.
EJ251 owners sometimes replaced their HG with the 11044AA642, MLS, used in the 04-05 EJ255 and 04-06 EJ257.
Now, for some reason I read that EJ253s can use the 11044AA670, itself used in the 06-08 EJ255. Can't confirm that though.
To add to the confusion, there is also the 11044AA770, used in the EJ257 2008+ - although it appears to look the same as the 670.