You can fab one, pretty easilly. But.............. The units from Bargain Fittings are complete and ready to install for not much more and are fer sure stainless and safe to use. They just upgraded them to 1/2 sight glass from 3/8th so that is a nice improvement for no extra money. Why re-invent the wheel, when some one has done the leg work and made a nice, cheap kit already? Just sayin....
Bob