it stops the wheel falling out if ever the axle nuts come loose
I've got those on my '89 Courier Comp - I think they are the best thing ever - never need to worry about the front wheel falling off!
Bikes: '92 Alpinestars AL Mega DX, '93 Cannondale M2000, '94 GT Zaskar, '90 Saracen Tufftrax (Pink!), '9? Raleigh RSP Team Edition 853
Projects: '89 Muddy Fox Courier Comp , '93 Raleigh Apex, '92 Cannondale M2000, '91 Scott Boulder, '87 Raleigh Ozark, '89 Raleigh Avanti, '87/88(?) Marin Palisades Trail, '91/92 Saracen Conquest E Stay, Unknown Saracen (1994?) Frame...