Thread for Merc 140 Riser Plug?

[myoldboat2]

I need to tap the hole in my riser elbow, where the brass pipe plug is supposed to thread into. It's kind of jammed in there now. Does anyone know the thread size? If I have to go bigger, what's the next logical plug thread size? I'm not a thread size guy.... thanks.

 

[Bt Doctur]

Re: Thread for Merc 140 Riser Plug?

1/4 x 18 NPT now. Could go 3/8ths NPT
http://www.engineersedge.com/manufacturing/pipe-tap-drill-chart.htm

 

[myoldboat2]

Re: Thread for Merc 140 Riser Plug?

Excellent, thanks for the quick reply.

 

[myoldboat2]

Re: Thread for Merc 140 Riser Plug?

Oops, one more question based on the chart you linked to.

Are the female threads in the riser taper or straight?

 

[Bt Doctur]

Re: Thread for Merc 140 Riser Plug?

Most if not all threaded pipe fittings, pipe, plugs are tapered. NPT .National Pipe Thread Regular bolts are straight. Some applications like your Alpha shift cable are 1/4 x18 NPST. the "S" meaning straight tap

 

[myoldboat2]

Re: Thread for Merc 140 Riser Plug?

Got it, thanks again.