kz900 turbo

I am building a kz900 turbo prostreet bike. I am getting ready to modify the oil gallery block . I have some old instructions from Mr Turbo that show where to drill the hole for the oil feed line and then remove the oil pressure switch and tap for 1/4 inch npt for an oil restrictor. The oil restrictor is basically a 1/4 pipe plug with a hole drilled through the center. I need to know what size the hole is. It doesn't say in the instructions...it just says don't mess with the size of the hole, it's been carefully calibrated . If anybody with a turbo bike knows or could check I would really appreciate it. Thanks

The restrictor hole through the 1/4 NPT plug is 1/4 inch or 6.3mm ( 6mm will do )

Thanks Zed!

I was going to ask the same question @Zed1015 Thanks

The hole size in the plug is 1/4in. if the turbo is a rajay turbo. If your using another brand the restriction may need to be a different size depending on the type of bearings in the turbo.