A zip fastener, comprising: first and second sliders (10, 11) disposed to slide lengthwise along a pair of stringers (12, 13), the sliders (10, 11) being moveable relative to one another between a closed position wherein the sliders (10, 11) are adjacent one another, and an open position in which the sliders (10, 11) are spaced apart to open the zip fastener; first and second pull tabs (15, 115, 215, 315, 16, 116, 216, 316), each on a respective one of the first and second sliders (10, 11), the first and second pull tabs (15, 16) being of like form; a first coupling connecting the first pull tab (15, 215, 315) to the first slider for rotation about a pivot axis extending substantially in the lengthwise direction of the stringers (12, 13); characterized in that: the first and second pull tabs (15, 115, 215, 315, 16, 116, 216, 316) each have a body elongated between opposing proximal and distal ends, and each of the first and second pull tabs (15, 115, 215, 315, 16, 116, 216, 316) includes a hook disposed between its proximal and distal ends, a tip of the hook being spaced from the body, such that a female locking feature comprises a recess between the body and the tip of the hook, and a male locking feature comprises at least a complementary portion of the body of the other of the first and second pull tabs (15, 115, 215, 315, 16, 116, 216, 316), which complementary portion may be received in the recess, such that with the sliders (10, 11) in the closed position, rotation of the first pull tab (15, 215, 315) about the pivot axis mutually engages the male and female locking features (21, 22) to interlock the first and second pull tabs (15, 115, 215, 315, 16, 116, 216, 316) in an interlocked position that prevents movement of the sliders (10, 11) to their open position. first and second sliders (10, 11) disposed to slide lengthwise along a pair of stringers (12, 13), the sliders (10, 11) being moveable relative to one another between a closed position wherein the sliders (10, 11) are adjacent one another, and an open position in which the sliders (10, 11) are spaced apart to open the zip fastener; first and second pull tabs (15, 115, 215, 315, 16, 116, 216, 316), each on a respective one of the first and second sliders (10, 11), the first and second pull tabs (15, 16) being of like form; a first coupling connecting the first pull tab (15, 215, 315) to the first slider for rotation about a pivot axis extending substantially in the lengthwise direction of the stringers (12, 13); characterized in that: the first and second pull tabs (15, 115, 215, 315, 16, 116, 216, 316) each have a body elongated between opposing proximal and distal ends, and each of the first and second pull tabs (15, 115, 215, 315, 16, 116, 216, 316) includes a hook disposed between its proximal and distal ends, a tip of the hook being spaced from the body, such that a female locking feature comprises a recess between the body and the tip of the hook, and a male locking feature comprises at least a complementary portion of the body of the other of the first and second pull tabs (15, 115, 215, 315, 16, 116, 216, 316), which complementary portion may be received in the recess, such that with the sliders (10, 11) in the closed position, rotation of the first pull tab (15, 215, 315) about the pivot axis mutually engages the male and female locking features (21, 22) to interlock the first and second pull tabs (15, 115, 215, 315, 16, 116, 216, 316) in an interlocked position that prevents movement of the sliders (10, 11) to their open position. the first and second pull tabs (15, 115, 215, 315, 16, 116, 216, 316) each have a body elongated between opposing proximal and distal ends, and each of the first and second pull tabs (15, 115, 215, 315, 16, 116, 216, 316) includes a hook disposed between its proximal and distal ends, a tip of the hook being spaced from the body, such that a female locking feature comprises a recess between the body and the tip of the hook, and a male locking feature comprises at least a complementary portion of the body of the other of the first and second pull tabs (15, 115, 215, 315, 16, 116, 216, 316), which complementary portion may be received in the recess, such that with the sliders (10, 11) in the closed position, rotation of the first pull tab (15, 215, 315) about the pivot axis mutually engages the male and female locking features (21, 22) to interlock the first and second pull tabs (15, 115, 215, 315, 16, 116, 216, 316) in an interlocked position that prevents movement of the sliders (10, 11) to their open position.