This will loop through all fields in a specific table:

[VBA]
Sub TableLoop()
Dim db As DAO.Database
Dim tdf As DAO.TableDef
Dim fld As DAO.Field

On Error GoTo ErrHandler

Set db = CurrentDb
Set tdf = db.TableDefs("tblTest")

For Each fld In tdf.Fields
' your code here
Next fld

ExitHere:
On Error Resume Next
db.Close
Set fld = Nothing
Set tdf = Nothing
Set db = Nothing
Exit Sub

ErrHandler:
MsgBox Err.Number & ": " & Err.Description
Resume ExitHere
End Sub

[/VBA]

If you want to perform the same actions on all tables you could do the following:


[VBA]
Sub TableLoop()
Dim db As DAO.Database
Dim tdf As DAO.TableDef
Dim fld As DAO.Field

On Error GoTo ErrHandler

Set db = CurrentDb

For Each tdf In db.TableDefs
' usually don't want to change system or temp tables
If LCase(Left(tdf.Name, 4)) <> "msys" And Left(tdf.Name, 1) <> "~" Then
For Each fld In tdf.Fields
' your code here
Next fld
End If
Next tdf


ExitHere:
On Error Resume Next
db.Close
Set fld = Nothing
Set tdf = Nothing
Set db = Nothing
Exit Sub

ErrHandler:
MsgBox Err.Number & ": " & Err.Description
Resume ExitHere
End Sub

[/VBA]