I still > don't trust the postal folks (or at least their machinery) not to do some > damage. http://pe.usps.com/text/dmm300/601.htm#1196660 3.3 Odd-Shaped Items in Paper Envelopes Pens, pencils, key rings, bottle caps, and other similar odd-shaped items are not permitted in letter-size or flat-size paper envelopes unless they are wrapped within the other contents of the envelope to streamline the shape of the mailpiece and prevent damage during postal processing. If an odd-shaped item is not properly wrapped, it could burst through the envelope and cause injury to employees and damage to USPS processing equipment. Odd-shaped items that are properly wrapped within paper envelopes and sent at letter prices may be subject to the nonmachinable surcharge under 133.1.5 or 233.4.3 for First-Class Mail letters, or the nonmachinable prices under 243.5.5 for Standard Mail letters. Certain types of odd-shaped items, when properly wrapped, are permitted as automation price letter-size mail subject to the standards in 201.3.0. Flat-size automation price mail is subject to the uniform thickness requirement in 301.3.0.