You're all wrong as that applies to goods brought in by hand. If you're importing by post from non-EU the rules are:

All other goods
If you order or send purchased goods other than alcohol, tobacco, perfume and toilet water from a country outside the EU then you:

- don't have to pay Excise Duty

- may have to pay Customs Duty on goods with a value that exceeds 135

- will have to pay import VAT on goods with a value that exceeds 15

Note that on all goods from outside the EU, Customs Duty is waived if the amount of duty calculated is 9 or under.

Customs Duty varies from 0% to 85% depending on type of goods. The rates are available using the online trade tariff site, which is pretty impenetrable... But a stepper motor would be 2.7% (i think)