Nikon SB-10 Instruction Manual page 21

Wide-Flash Adapter 5W-2
Clips easily over the reflector of the 5B-1O to
increase the angle of flash from the normal 56°
to 67 ° when positioned horizontally and from
40° to 48° when positioned vertically . It also
ensures adequate lighting at the perimeter of
the viewfield when the 28mm wideangle lens
is used. Reduces the guide number to 18
(meters) with an ASA 100 film on manual.
Battery Holder M5-2
Handy holder to accommodate spare batteries .
21