... made of borosilicate 3.3 pyrex male and female clear, blue, green, yellow, amber, pink, purple lab use Ground glass joints of borosilicate 3.3 pyrex are used ... the ends, except for stoppers.Glass ground joints of borosilicate 3.3 pyrex types:Conically tapered jointsBall-and-socket joints glass ground joints of borosilicate 3.3 pyrex