How To Grant Folder permissions for WMSvc IIS

Im using Web Deploy with IIS7 and I want to grant permissions on a web site physical folder.

Ive done this before (as I have another physical folder with r/w for WMSvc) but I have forgotten how I did it!

When I go to the physical folder > Security Tab > Edit > Add > Object Name = WMSvc > Check Names, I get 'An object named WMSvc cannot be found'??

I have the 'WMSvc' object listed fine in the 'Groups or usernames' on the other Folder I mentioned above.

I feel a bit daft, what am I doing wrong, how can give folder permissions to WMSvc object on a physical folder?

Not sure if you ever found it, but you need to enter:

NT Service\WMSvc