I'm a little uneasy about silicone or brass within the boiling water of my Bonavita, so I decided to make a flow restrictor out of 316 grade Stainless Steel. I basically made a 1/4" long bushing with an outside diameter of .265" and an inside diameter of .135". I also tried an inside diameter of .165". The flowrates I got were as follows:
Stock 1.0L or 1.7L Bonavita kettle: 2.2 lpm (liters per min)
.165" inside diameter restrictor: 1.0 lpm
.135" inside diameter restrictor: 0.7 lpm
I did a little research, and found that an off the shelf #8 stainless steel spacer will also work as a flow restrictor. The inside diameter of the bushing will be about .166" which will give about 1.0 lpm (half the normal flowrate). The outside diameter is .250" (1/4") so I recommend the 1/2" long spacer so it will firmly fit deeper within the inside of the gooseneck. A #8 spacer is about $1.00 from Mouser.com or McMaster.com (McMaster usually charges a lot for shipping). Here is a link to the off the shelf spacer that I recommend:
http://www.mouser.com/ProductDetail/RAF ... /1128-8-SS
If you prefer a smaller hole for more restriction, then look for a #6 or #4 stainless spacer. The #6 will yield about 0.7 lpm and the #4 even lower. Links are below:
http://www.mouser.com/ProductDetail/RAF ... /1128-6-SS
http://www.mouser.com/ProductDetail/RAF ... /1128-4-SS
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Thanks for all the research, Doug. I just ordered two stainless steel flow restrictors for less than two dollars !