Slide Fastener

A slide fastener comprising:

• a pair of tape members disposed in parallel in a left-right direction,
• a pair of fastener element rows attached to core strings which are arranged along opposite tape-side edges of the tape members, and
• a slider into which the pair of fastener element rows are inserted, the slider that engages and disengages the pair of fastener element rows,
• wherein each of the fastener element rows is composed of a plurality of fastener elements,
• wherein each of the fastener elements includes a design portion disposed at a front side of the tape member, and an engaging portion disposed at a rear side of the tape member so as to engage with adjacent fastener element,
• wherein the slider includes:
• an upper blade and a lower blade, which are disposed in parallel and distant from each other in an up-down direction;
• upper flanges provided along left and right side edges of the upper blade, respectively;
• lower flanges provided along left and right side edges of the lower blade, respectively;
• a guide post connecting the upper and lower blades;
• and
• a substantially Y-shaped element guide passage surrounded by the upper blade, the lower blade, the upper flanges and the lower flanges, and having shoulder mouths and a rear mouth,
• wherein plate thicknesses of the upper and lower flanges are smaller than a distance between adjacent fastener elements, and
• wherein a dimension of a gap between the upper and lower flanges in the up-down direction is smaller than a dimension of the core strings in an front-rear direction when the core strings pressed with a pressure of 5 kgf.