Wire-to-turnbuckle size

[Brion Toss]

Hello,
The available pin sizes are there to accommodate different wire constructions. The pins should always be at least a third stronger than the wire (as should turnbuckles, tangs, chainplates), and 3/8" is right for 1/4" 7x19 and 7x7. But it is barely stronger than1/4" 1x19, which is why the 1/2" pin is the correct size.
What too often happens is that builders will simply decide to save money, putting swages (and turnbuckles, tangs, chainplates) meant for 7x19 onto 1x19, with predictable consequences for safety factors. Similarly, they might choose aircraft eyes and forks instead of the spendier marine ends. Make sure of your wire size -- perhaps you don't really need 1/4", for instrance -- and then choose components to suit.
Fair leads,
Brion Toss