# 4 (Practical Invisible)
The third largest in the family of 3k metal zippers.
The width & thickness of #4 zippers is 4.90mm x 2.15mm .
#4 zippers are not very widely used in the world since the advent of the Customized #4.5 zipper which is a direct substitute for #4 zippers.
The #4 zippers are regularly used as denim fly zipper & generally with a spring lock slider.
3k standard crosswise strength.
#4 Brass – 63 Kgs.
#4 Aluminum – 35 Kgs.
#4 Nickle silver – 68 Kgs.
#4 invisible zippers are very rarely used in open end application.
Standard complaints of #4 zippers arise in washing & ballooning of garments. The main way to avoid damage to these zippers is to buckle up the button or the flap by a stitch to prevent the load of the garment on the slider.
The B.S. 3084:2006 recommends that #4 zipper in invisible which has to be used in specification A, B & C to have latent cross wise strength of 15, 20 & 25 Kgs respectively. 3k satisfies this comfortably.
For details of British Standards & #4 Zippers Test charts, click here.
For Wash Care Instructions, click here.