My boost gauge has a 4mm dia fitting on the rear of it. My boost gauge nipple on my egr pipe is 6mm. Can I get an adapter and use 6mm and 4mm hose, or will 4mm vac hose stretch over the 6mm fitting

I take it using 6mm hose would be no use as it will be too loose on the gauge?

 

I used 4mm silicon hose on mine and it went on the 6mm outlet fine, not sure about rubber hose though

 

cup of boiling water, dip 4mm hose in it till soft and supple, push on 6mm fitting.. simples

 

Cheers, will give that a go