Thanks to boatmadman, for the link to number 3 gas jets. I had give up searching for this small size, about a year ago, they seamed to be unavailable. My boiler design was for number 3s. I am using number 5s at present & the flame tends to blow right through the fire tube, burning at the top of the funnel. I have made a gas pressure regulator but this is only part successful. I have placed an order.