What size screw is reg gauges?

[M600]

i need to get a blanking plug to get rid of the gauge on my reg, not bottle reg.
is it 1/8th or 1/4th size?
im getting it from here...
http://www.kiowa.co.uk/Products/Hydraulics/Hydraulic_Adaptors/Plugs_&_Caps/BSP_Blanking_Plug
any help is good
thanks

 

[Oily]

1/8 npt

 

[Tom Allen]

pm me your address and i'll pop one in the post to you.