These are hand-down the best valve guides you can buy for your U20...A few bucks more, but you get what you pay for.   They will probably outlast the rest of your engine - do it once-do it right and forget about it!
 
100% Made here in USA on a CNC turning center from the finest German silicon-bronze.
 
We make these by the 100's so they are always in stock.
 
Unlike cheaper "service quality" guides sold by others, these are precision machined from the best guide alloy you can buy.
 
These guides support either stock Nissan "hat seals" or modern teflon seals. Greatly improved metallurgy over cast iron and no-name brands.