Used on platens or cylinders.  

The standard machines have 6 wheels and are designed as:

• high plunger for the platen 
• low plunger for the cylinder
• forward or backward
• Roman or Gothic
• usually with 4 mm characters

Machines can be supplied with:

• Smaller or larger characters
• More than 6 wheels
• Only 2 wheels to number 1- 50 or 50 - 1
• Only 3 wheels to number 1 - 100 or 100 - 1 etc.