1. Are these your files generated from a CAD tool? If yes, I would strongly encourage you to re-export the Gerbers as 274X and everything will be fine. However if this is customer generated data than we can proceed by updating the Apertures.
Note: The old Gerber 274D format (from the 1980's and before) is obsolete and deprecated, plus strongly discouraged by the PCB industry - due to potential operator errors and misinterpretation. For example, the aperture list just states THER (without any further parameters -- # of spokes, width of spokes, etc.). I do not believe the Thermal should be 4 lines as shown in the Gerber viewer. IT should have the following appearance.
https://numericalsoftware-update.s3.amazonaws.com/tutorials/2016-01-12_14-22-53.pdf
2. A generic Thermal will have 4 spokes (at 45 degree angles) and the spoke gap width will be equal to 1/2 (OD-ID).
Here's a tutorial how to perform edits on FAB 3000 to add Thermal:
https://numericalsoftware-update.s3.amazonaws.com/tutorials/2016-01-12_14-41-18.mp4
Note: We have updated FAB 3000 to automatically add 4 Spokes and assign the Gap for 274D Thermals when no parameters are available. This will allow you to easily import all 274D files and get the desired thermals your require.
Numerical Support Team