Hello
Firstly may I suggest turning on the remove padding option for this area of your template (top-1) within your templates parameters (Module Widths tab). Your icons should auto width to fill the area provided presuming you have your icons set to 3 columns. Regardless you can add the following to the Custom CSS field of your templates parameters which will set this for you...
.j51_icons855 .j51_icon {
width: 33.3%;
}
.j51_icons855 .j51_icon:last-of-type {
border-right: medium none;
}
CiarĂ¡n