The list of changes published on the 28th March 1924 made a change to the 190 pattern bayonet frog. The decision had been taken to drop the Sirhind type entrenching tool and so the carriers for the head and helve were no longer needed. As a consequence the tab on the rear of the bayonet frog could also be delted and removed as not needed. From this point onwards new manufacture would delete the tab, and existing frogs would be modified to drop it.
Today we are looking at a late World War One frog that has had its rear tab removed to make it into the fourth pattern:

We know that this is a late World War One frog as it has had the two reinforcing rivets just above the loops to hold the bayonet scabbard deleted, this being an economy measure introduced around 1918. Apart form this, the two loops are standard and designed to fit either side of the teardrop shaped frog stud on the scabbard:

It is interesting to note the patterns of wear on this bayonet frog. The webbing is frayed where the bayonet frog stud passes through, with rust staining suggesting a scabbard sat in the frog in the damp for a considerable period of time. This rust stainign is also visible at the top of the loops, where the cross piece of a bayonet would rest and at the top of the frog where the pommel would also be in contact with the webbing:

All this suggests that a bayonet and its scabbard were left in the frog for at least several years at some point in the last century.
The top of the frog has a simple three inch wide loop to allow the 08 belt to be passed through:

The 1908 fitting instructions include the following description of the frog:
Frog: This consists of a loop to slip on the waistbelt and a body fitted with two horizontal loops. The scabbard is insereted and pushed through until the stud on the outside comes out between the two loops.