Leading edges (204) of concentric members (202) are desirably hidden in unions of two concentric members (102, 202) intended for advancement through the vasculature for vasculature implant delivery. Grooves (104) or impressions on the inner concentric member (102) provide spaces for the leading edge (204) of the distal tip of the outer concentric member (202) to create edgeless unions of two concentric members (102, 202) for safe and unimpeded advancement and operation of vascular implant delivery devices which include the two concentric members (102, 202).