Transom holes, what size to drill?

**LakeFever** · 06-30-2022, 08:12 PM

im making a transom drill guide plate and stopped tonight at what size to drill the holes? Typically i go one size over for bolt holes so a half inch bolt would be 33/64 or even 17/32 which works great. My transom is coosa so i wont be doing epoxy in the holes i will be installing 1/2” fine thread studs with brass nylocs. I’ll be sealing the holes with 5200 or 4200 im undecided on which yet but probably 5200 because the studs can stay if i change up jack plates later on although thats unlikely because i bought a new seastar.

anyways what size should i drill the holes? Im thinking spot on half inch might be best but I want to hear from you guys before i commit to that. Thanks

**LakeFever** · 07-01-2022, 10:10 AM

I dont know what happened to my one and only 33/64” drill bit but I tested in a scrap piece of 3/4” coosa with a 17/32” hole and a 1/2” hole and the 17/32” is too large the 1/2” 316 rod im making the studs out of wobbled around way too much for my liking. While the 1/2” was tight being zero clearance I feel more confident with it so thats the direction im going. Feel free to chime in any other thoughts about this maybe it will help someone else.

**LakeFever** · 07-01-2022, 01:02 PM

Definitely happy with half inch holes. Made a new engine stand for my new motor so i tested my transom drill fixture guide plate deal out. Worked slick and made this very easy. Plate is 16”x12” with bia pattern and a tiny hole dead center to aid in alignment. The blocks are 3/4” plate. I laid out the drill pattern on the 1/8” cold roll plate using a scribe for accuracy, marked, center punched, then drilled with a 1/16” bit. I cut the 3/4” plate by eye around 1” square pieces and clamped them to the plate, used a mig to tack them in place. Then using my pre drilled 1/16” pilot holes i drilled them out to half inch on the drill press