Here's how to print only the horizontal gridlines in an Excel worksheet:

1. Open the Excel worksheet that you want to print.
2. Click on the "Page Layout" tab in the ribbon at the top of the screen.
3. Click on the "Sheet Options" button in the "Page Setup" section.
4. In the "Sheet Options" dialog box, under "Gridlines", uncheck the box next to "Vertical".
5. Click on "OK" to close the dialog box.
6. Click on the "File" tab in the ribbon.
7. Click on "Print" in the left-hand menu.
8. In the "Settings" section, click on the drop-down menu next to "Print Active Sheets".
9. Select "Print Selection" from the drop-down menu.
10. Click on the "Print" button to print the worksheet with only the horizontal gridlines.

That's it! Now you should have a printed copy of your Excel worksheet with only the horizontal gridlines. Let me know if you have any other questions or if there's anything else I can help you with.