The brass barbs are very close to the end of the block, so had I presed barbs in on the end they would have interfered with the brass barbs at the front.. You don't need sealant as long as the tolerances are tight enough. The block was drilled 6mm and the brass barbs were turned to 6.20mm, so slightly under a .20mm tolerance. The aluminium I used is 6061 grade, so the barbs can be lightly larger than if they were pressed into cast aluminium as on carb bodies. There are a number of other considerations, but that's about it.