The range of a thermometer and it reading accuracy is dependent on the size of the hole,
the length of the tube and the fluid in the thermometer. Typically the smaller the reading
increment, the less range it will have. As an example, a 0.1° C accuracy mercury
thermometer with a range of 100°C will typically be about 600 mm long. The
restrictions rest with how well the maker can fabricate a readable scale. To increase
readability some manufacturers have moved to non-round thermometer bodies, The
rounded corner on the reading side acts as a magnifying glass, making the liquid column
show up wider, and easier to read. The round thermometer is still the standard and there
are a variety of holders and seals to fit them. There are also armored sleeves to put them
in that allow them to be used, but reduce the chance of breakage.
The chart below lists some thermometers commercially available. These are clearly not
all the thermometers available, but a limited selection to give you some idea of what
some more standard sizes and ranges are.