#6 3/4 Security Tinted Self-Seal Envelopes - No Window, Size 3-5/8 X 6-1/2 Inches - White - 24 LB - 300 Count (34300)

I've used thousands of these envelopes (this brand) over the years and I can say they are the best around and at a really good price. Also the number 9 and 10 double window are awesome.

Smooth sailing, the size that I ordered...