What do I use the Classic strangifier with?

I just unlocked a Mann Co. Supply crate key and got a "Classic strangifier", which apparently changes normal items to strange items. However, when I click "Use with...", it says that I have no eligible items to use with the strangifier. I've been playing for a while and have plenty of weapons. How can I use this?

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What do I use the Classic strangifier with? - Content female customer with long curly hair wearing casual outfit sitting at wooden table with netbook in classic interior restaurant while making online order

What do I use the Classic strangifier with? - Vintage TV set on wooden bench

What do I use the Classic strangifier with? - Vintage TV set on floor near wall

What does a Strangifier do?

When the Strangifier is used, the user will be prompted to select an item within their inventory. Upon confirmation, the Strangifier will be consumed and the selected item will be converted into one with a Strange quality, keeping the item's custom name or description, if it has one.

Can you Strangify war painted weapons?

Unless the War Paint is Civilian grade, no. And weapons that have strangifiers and are applicable for war paints cannot work either, as this was patched months ago.

How do you make something strange in tf2?

Methods of obtaining Strange items include:

Unlocking a Mann Co. Supply Crate containing the item,

Using a Strangifier on an item,

Purchasing the items from the Steam Community Market,

Earning Botkiller weapons or Australium weapons from Mann Up mode,

Trading with other players for them.

Tf2 - Crafting a Collector's Classic + Using Classic Strangifier

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Images: Ono Kosuki, Yan Krukov, Anete Lusina, Anete Lusina