1/8 nps is the same as 1/8 ip... or 1/8 ips .
( they are both parallel sided , not tapered 27 tpI )
nps > national pipe straight
IP .>.Iron Pipe
IPS iron pipe straight
straight threads are not sealing threads , a gasket or o-ring provides the seal and the threads compress the seal
IP is an American thread standard , allowing interchangeability
for lighting fixtures , from about 1900 .
As an obscure thread
it lives with most of us in our homes without our even knowing it
taps and dies for 1/8 ip are available ( because wall lights , lamps and chandeliers are still being made)
and short lengths 1/8 ip pipe are available at almost every local North American hardware store .
( I don't know about Europe or UK )