Do 20 Gauge, 1.5" Terumo Luer lock syringe combos have interchangeable needles or are they permantly attached? I thought I could purchase the 20 gauge 1.5 inch combos to draw with along with some 23 gauge needles seperately for injection.

Not sure if I made the right descision or if buying syringes w/o needles along with two seperate sets of needles would have been the right choice.