Soldering Iron

https://backpack.tf/item/4727686541

Sale 1) ?

https://backpack.tf/profiles/76561198197481041#!/compare/1540166400/1540684800

https://backpack.tf/item/2473399087

Sale 2) Bulk sale

https://backpack.tf/profiles/76561198322414616#!/compare/1547510400/1547596800

https://backpack.tf/profiles/76561198418740133#!/compare/1547510400/1547596800

https://backpack.tf/item/5048820034

Sale 3) Sold for a Well-Worn Specialized Killstreak Hot Cabin Fevered Sniper Rifle

https://backpack.tf/profiles/76561198024867201#!/compare/1542240000/1542326400

https://backpack.tf/profiles/76561198126777328#!/compare/1542326400/1542412800

Using for the Sniper Rifle.

Sale 4) Sold for an Australium Sniper Rifle (22.5 Keys)

https://backpack.tf/profiles/76561198126777328#!/compare/1543881600/1543968000

https://backpack.tf/profiles/76561198065028772#!/compare/1543708800/1544140800

The Sniper was recently priced when this sale happened, so this sale rounds to 23 Keys

Sale 5) ?

https://backpack.tf/profiles/76561198065028772#!/compare/1543708800/1544140800 - Doesn't go later

https://backpack.tf/profiles/76561198833242874#!/compare/1544918400/1545696000 - Doesn't go earlier

Sale 6) Bulk sale

https://backpack.tf/profiles/76561198080436316#!/compare/1547683200/1547769600

https://marketplace.tf/items/30004;5;u33 - Sold for $41.98 when Keys were ~$1.75 each

https://marketplace.tf/items/5021;6/Mann%20Co.%20Supply%20Crate%20Key

41.98 / 1.75 = 23.98, which rounds to 24 Keys