Fastener Size
I would be careful about adding sizes that are not in the standards just in case there are not available to buy first. Then if you need exact dimensioning refer to a drawing or chart.
The simple way I added the size is to ensure you have the family in a writable library then place as custom the next size up. Modify the Parameter's "NLG" (Nominal Length) and the "GEL" (Thread Length)
In this case GEL needs to be less than the Nominal length or the sketch will fail. NLG =30mm ,GEL= 28mm
Now that you know the bolt can be modelled using the changed parameter, jump back into the CC table and add a new row. Copy the 45 mm length row and paste and change the file name /description etc to ref 30 mm size.
In the CC table you will see a column Grip Length this has an expression in it {NLG}-{GEL}. This equates to the non threaded portion of the bolt see link . I am not sure if you need the Grip length changed in the CC table but just in case enter the difference in this cell. Save the table and your done.
Of course I didn't follow the exact steps above at first, I changed the CC table first columns(Nominal Length and Thread Length and tried to place the bolt but the sketch failed due to the GEL parameter being too long. If this happens to you ensure you hit refresh from CC in the assembly editor to pull through the changes when you find the parameters that work.
I would suggest trial all your parameters in a custom placed part first and then place them into the CC table.
Just be aware that if you modify or use linked families in Content Center, when you upgrade to a new version it can mess up any changes you've made.
They exist in real life so it's odd that it's not on there.
Inventor Certified ProfessionalAs @SharkDesign has said be careful of linked families.
Right click family and save copy as and select independent family. Content will be isolated from out of the box content and will not be effected by release migration.
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