Column width in textarea not working

I have lloked at documentation, FAQs and tried every combination but can’t seem to restrict the length (Columns) of the field on the form. I want to put two names on one line and restrict the length of the field.
[textarea* fieldname 10×1 default:user_first_name]
The x1 works for setting the rows but the 10 or any other number does nothing?

https://wordpress.org/plugins/contact-form-7/