Joined: Jan 2010
Posts: 9,834
Likes: 1,811
From: Northern California
Bikes: Cheltenham-Pedersen racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.
Sounds like a Normandy tool, the large-diameter spline.
Most established older shiops should have that tool, since these tools don't wear out like many others can.
I'm up here in the foothills and have the Normandy/Atom tool here.