j_omega,
I send parts to a Chinese factory several times a year. Here's what I recommend.
Send with a well known international courier (DHL, UPS, Fedex), never use the postal service. You are selling goods to your 'customer' in China - include a commercial invoice. This contains description, country of origin, price, quantity, and HS tariff code. Price can be anything. Quantity doesn't have to match the quantity of goods in the package, but try to not be more than an order of magnitude off. Adjust the price/quantity so the total value ends up being about USD 50/kg. Never include more than five line items. If you have more, just put the first five and leave the rest off the paperwork.
The receiver pays something like 17% tax on the value declared. I usually didn't bother to put HS tariff numbers until about a year ago when the courier/customs changed the recipient some ridiculous extra fees on one shipment. Now I put the code 8542.39 on every item and haven't had any trouble since.