Selecting shells is one of the most difficult things with owning crabs. You can pick what you think are ideal shells, but the crabs won't like them. Knowing how to read a tape measure down to at least 1/8" will help a lot. Even using callipers will make it easier. You may even want to Google "fraction to decimal graph".
Naples has good information on how to measure shells. That info is pretty standard.
http://naplesseashellcompany.com/sizematters.html
You will need to "try" and measure the shell openings of your crabs. Try to measure to the nearest 8th inch.
This is where it is pure luck. If the shell openings are one inch or smaller we will purchase several shells 1/8" and 1/4" larger.
Here's an example.
If your crab is in a 5/8" opening, we will order 3/4" and 7/8" openings. Every crab is different at what they like so offering several of each size is usually best. Each shell even the same size will be slightly different in weight and shape. Crabs know the difference. Be sure you pick popular type shells to increase your chances.
Here's the guide for favorites!
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