Originally Posted by JTJ
Combination squares come with a needle like you described. Price range is $5-$50. You could also buy a scratch awl or an ice pick. You can also get heavy pins with ball ends at craft stores. I have also found that an Exacto knife works quite well.
I would much rather use a blade for layout lines but I need a centered point for this. I will check my square... That may be where I saw what I've got in mind!!!!
Here is a center finding gauge that is similar to what I want to do (the first little gauge after pressing play and not the one shown):
Rather than a hole in the center for a pencil I want to put two pins in equal distance on each side of center. That would let me scribe two parallel lines and their width would always be in proportion to the thickness of the board. That way I wouldn't have to measure the thickness of the board and then calculate the width of the tenon. So I need a pin that is almost like a short dowel but with a needle sticking out.
And the gauge in that Youtube clip can be modified by putting dowels at various widths on each of the 4 sides of the gauge. That lets you use it on different width boards without all the extra space like in that one.