A synchronous belt drive transmits torque through the positive engagement of belt teeth (as opposed to frictional surface contact). The advantages include reducing drive slip and belt stretch in an arrangement where metal to metal contact is eliminated and therefore lubrication is not required and noise reduction is significant.

The reference number B648M20SDS denotes: -
B Browning.
64 Number of teeth.
8M Pitch designation 8mm.
20 Belt width in mm.
SDS Bushing designation.

From the manufacturer's catalog, a table is provided showing the various sizes available for an 8M20 unit. Using the figure shown below it can be seen that there are seven larger sizes available and the largest B1448M20SF having 144 teeth and a pitch diameter of 14.447” (The table shows 114 teeth which is a misprint).
https://www.mrosupply.com/synchronous-pulleys/2279167_b1448m20sf_browning/
https://www.mrosupply.com/search/?q=%22browning+hpt+sprocket%22

The table below shows the Browning bushing types.

The manufacturer’s technical literature always provides useful information for the selection, installation, and operation of timing pulley drives. These catalogs guide you through the process and will consider the applications load and service factors, speeds and transmitted torque & power values, etc. Certified drawings will also provide accurate key dimensions to ensure a problem free design and installation process.
The description with the diagram shown below forms only one part of the selection and installation procedure from the drive manufacturer and may be specific to this design of pulley only. These tables ensure the selected drive components are sufficiently robust in operation to provide a long and reliable service life and therefore must be strictly adhered to.

In this case, the midpoint deflection force for an 8mm pitch and 20mm wide belt is 4lbs.
A final point to note is that changing the diameter and number of teeth on a pulley will affect the speed and load characteristics of the drive arrangement as well as requiring a new longer belt or a different centre distance setup as an alternative.