Custom machined exhaust emission  port plugs.  Eliminates the funny exhaust chirp caused by removing the exhaust port tubes.  Excellent US-made CNC lathe parts machined from AL and brass. 
 
Only a couple dollars more, but these won't rust, seize or look crappy.
 
These are the best, You get what you pay for!
 
(These are not incorrect pipe plug fittings, these are the proper threads for the cylinder head)
 
No Chirp, great quality!