Blackheart Crossbow String 35 1/2 in. Parker. These bowstrings feature GlideLock center serving which enhances durability reduces friction reduces serving separation and almost eliminates the ridges between the serving strands. The DuraWeave process includes pre-stretching the strands resulting in highly consistent string length. Each string is meticulously hand crafted to fit your crossbow. 26.125 for Excalibur Micro 335 Micro 335 Nightmare. Package Contents: Blackheart Crossbow String BlackHeart crossbow strings are crafted using the right blend of modern materials machinery and time-honored techniques. These bowstrings feature GlideLock center serving which enhances durability reduces friction reduces serving separation and almost eliminates the ridges between the serving strands. The DuraWeave process includes pre-stretching the strands resulting in highly consistent string length. Each string is meticulously hand crafted to fit your crossbow.