I did some further searching and I think the answer is that the type is actually the same ("uniqueidentifier"), but the default value and general setup are just done differently (Table ROWGUID not set for instance).
Assuming that to be the case, here's another question :
If I have two tables linked on a field (in this case HdrID - the unique ID of the header record) is it necessary for me to create an index of this field in the Detail record if I already have a Relationship Constraint set up?
Table Name=[tblTHSOPH] (AKA Header)
- Field Type IndexInfo
-
HdrID uniqueidentifier PK
-
Various Header related fields...
Table Name=[tblTHDSOP] (AKA Detail)
- Field Type IndexInfo
-
DtlID uniqueidentifier PK
-
HdrID uniqueidentifier FK
-
Various Detail related fields...