Choose node item from list and add to form
I'm not sure what kind of form your question is about. You say, you want to e-mail the result, so this is probably a Contact form.

Here you can add a reference field for content and then configure this field for the content type "Machinery". You can set this to unlimited values, so that you can add multiple machines. The default is an autocomplete field. You can change this to a select list in "Manage form display".