Doube wall thick white heatshrink for repairing iphone or samsung charging cable, refer to the list page state below. (no pen spring needed to reinforcement)

http://list.qoo10.sg/item/DOUBLE-WALL-HEAT-SHRINK-TUBING-FOR-MOBILE-SAMSUNG-OR-IPHONE-CHARGING/531599989

Photo below for H/P cable, refer to the above link, thanks.

Heat Shrink Tubing
Color : black
Shrink Ratio : 0.5
Wall thickness for 8mm diameter : about 0.3mm
Wall thinkness for 10mm diameter : about 0.3mm
Material : PVC
The item is mainly used for wire connection , solder joint protection , electronic device protection and insulation treatment , metal surface protection etc .

Reinforcement of iPhone charger cable instruction :

50% heat shrink tubing, example 8mm diameter tubing, can be shrinked to 4mm-7.9mm diameter.

For those people who don't know which size is for your cable or iphone cable, choose mix size, try and choose a suitable size before heat. use lighter to heat, don't put too near to the flame.
Mix size = +6mm diameter X 20cm + 7mm diameter X 20cm + 8mm diameter X 20cm + 9mm diameter X 20cm + 10mm diameter X 20cm = $2.00