Monarch , Fine Point Sterling Silver Mechanical pencil Propel-repel Engine - turned wave lined pattern Lead 1.1 mm (1 piece in pencil) Length 12.5 cm
Common Vintage Lead Sizes
The most common sizes of lead for vintage mechanical pencils were 1.1mm and 0.9mm. 1.1mm leads were frequently referred to as "thick" lead and the 0.9mm size was often referred to as "thin" lead. Of course, today, there are much thinner diameter leads made, but we're talking antique pencil leads!
For your reference:
1.1mm = 0.046 inches
0.9mm = 0.036 inches