201 - not suitable for being left outside on the clothes line 304 - can withstand some time outside, but not near the ocean 316 - marine grade is rust-proof.
There are a variety of sizes in the pegs:
Standard - your everyday peg that suits most needs
Windy - a slightly thicker wire for extra hold on the line in windy conditions
Very strong - as it says, super thick and strong hold, but is harder squeeze
Very long - just what you need for hanging larger items like pillows and bags
Largest - super hard core
Easy squeeze - for those with dexterity issues or find it hard to squeeze
Tiny - ideal for craft, hanging photos and little jobs around the home