Uses for 49.9Ω resistors?
If you need a 1% resistor, \$50\Omega\$ resistors are not a standard 1% value.  The nearest standard 1% value is \$49.9\Omega\$.  See http://www.rfcafe.com/references/electrical/resistor-values.htm for standard values and some explanation of how they're derived.

The equation for standard 1% resistors is: $$ R = 10^{d + \frac{i}{96}}$$ where \$d\$ is the (integer) decade number, \$1 &lt;= d &lt; 6\$, and \$0 &lt;= i &lt; 96\$.

It's the same for other precisions, except that instead of 96 for 1%, we use 48 for 2%, 24 for 5% and 12 for 10%.