GM big block engine drain plug size?

[carboncow]

My exhaust manifolds have the nifty plastic drain plugs you can remove by hand and I'd love to have these on the block two. My 1997 7.4L has the two drain plugs on the block. I forgot to measure them over the winter for thread/size before I put them back in but I"m sure these are standard for all GM blocks small or big.

Can anyone confirm what plastic plugs I can purchase for this need since I tried to test fit the exhaust manifold ones and they didn't appear to be the same tread/size.

Thx.

 

[Dieter]

The block drains are 1/4 npt the blue plastic plugs are 1/2 or 3/8 so there is normally and adapter that screws into the block http://www.marineengine.com/parts/m...000-thru-0k999999/cylinder-block-and-camshaft

parts 5&6 two each in this merc parts drawing should get you what you want

 

[bondo]

Ayuh,.... The block is 1/4" pipe, 'n the blue plugs are 1/2- 13,.....