Silicon intercooler/inlet piping sizes?

[Blazer406]

When you see these hoses advertised as "4" - 3-1/2" silicon reducer"...... are they referring to the ID size or OD size? My buddy needs a reducer to go from his 4" MAF pipe and connect it to a LS1 MAF meter. I understand the LS1 MAF meter is 3-1/2". I assume I need to be looking for a 4" to 3-1/2" reducer.... I know the clamp sizes are sized by OD range..... so you can't put a 3" t-bolt clamp on a 3" hose.....you need a 3-1/2" clamp.....

 

[mikestertwo]

I.D.