I'm an electrician and agree with the previous comments. Get the correct cord for your 240 volt dryer outlet. Using the incorrect plug on the incorrect voltages is asking for both trouble and safety. In general people assume that the plugs are correct for the rating given. That is why they created NEMA standard plug configurations and numbers. Spend a couple more dollars and get the right one. It could also save your welder in the future if you ever use it in another location or lend it to someone.
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