Any ideas why this is happening? I got a new bow and have had 3 nocks break. Thought it might be a bad lot, but I've shot the arrows in other bows with no problem. Could it be the string serving is a little to thick?

Looks like some very old nocks.

I had a batch of old 'white' Mercury nocks that were bad. They would crack and break and I ended up throwing a bunch of them away. Never had trouble with any color but the white and that was a long time ago. I suspect it's the nocks. Try flexing them a few times, it's likely they got brittle for one reason or another.

Those were very old nocks to begin with. Plastic deteriorates with age.

I thought it might be age also, but the third to break was a newer red one. I have also been flexing the nocks after each shot to see if they crack. That is how I found that the second one broke. The string is not seating all the way into the throat of the nock. I was thinking the string might act as a wedge on release. I have some some classic nocks that seem to fit the string better. I will probably use those nocks for this bow. I did have a batch of yellows that were rough and grainy in texture, those broke on a different bow. Those seemed to be a problem with that batch.

The string will act as a wedge and break the nocks if it is too thick.

So if you shoot them on other strings and they seat fine and don't break, but you shoot them on that string and they don't seat and break, then that seems the logical initial conclusion.

The string not fitting all the way into nock? For sure,your right in thinking the string os to wide for the nocks,causing them to break.

Replace the old nocks with new nocks and open them up with a file to fit the string properly. Nocks shouldn't break like that.

It is not just age. I have nocks from the 60's that are just as soft and pliable as they were over fifty years ago. It's more of how they are made, and maybe how much they were heated or cooled, etc. It seems to be more of a manufacturing anomaly than anything else. Whatever happened to the Mercury white nocks, they fixed after finding out there was a problem...and they weren't old then.

When you get any older nocks, or actually any new nocks, flex them in with your thumb and finger and see how they respond. It's really easy to see if they are usable or not. We get in trouble when we just take things for granted.

I had the same experience as George with a bad batch I bought. Broke a couple off the get-go and tossed the bag. No problems since or before that. Mercuries are all I have used for decades and have hoarded a bunch of them. Like you said and several others, reserve your string smaller to get a smaller served string that fits properly and your problems will likely go away.

I would think that not seating all the way would be a deal-breaker. That would be like leaving daylight between your shoulder and the butt-stock of a 12-ga stoked with a turkey load….

You could reserve with a smaller diameter serving.

Sounds like good advice above.

Also hard plastics break easier than softer plastics as far as nocks go.All plastic nocks are not created with the same plastic.Those look like Classic index nocks and thier made from harder plastic than the ones I prefer to prevent broken or cracked nocks.

Thanks Corax. That hurt these crispy ol' shoulders just to read it! LOL.

Good advice to check the nocks. I just had an old white one break on me, luckily while I was nocking the arrow, not while shooting, leading to dry fire.

So now, in addition to flexing/checking the carbon arrows (of which I use very few) we have to pinch the nocks. Any more items and I will have to make a checklist.

Yep...I quit using mercury nocks for that reason. Ruined one bow in the process!

Thanks for all the responses. I replaced the broken nocks with classics. So far no broken nocks.

I mostly use reinforced self knocks.Fresh modern plastic would probably be safer.your knocks should be snug but once clipped onto the string you should be able to hold the bow pointing down to the ground and tap the string with your finger to dislodge it.That is my test.Does your string seat fully into the knock ? If not the string may be breaking your knocks . Osr

I used to mold plastics and they could be made of a material called “Delrin” and it had a certain heat setting on the barrel to soften the raw material and it was finicky . In the cooling setting process it could be brittle as well. I doubt back then those nocks were checked but ever so offer . Little molds like that could probably make 25 at a time in a 30 second turnaround where mold opens ejects them out and closes then lock up for next batch. It would be hard for a person to check every single nock but if they looked good then they were packaged and sent out possibly but I didn’t work for a nock company but just my thoughts on it. Then as others have said like redddogge mentioned those nocks could be a bit tight on the string and May need just a little file work but that’s removing material. Some folks just heat up water not boiling hot and let it set in and it will relax the material and make it pliable enough to open the throat . I would do that then let it cool down and set the nock .It will get memory and should stay . Then again those nocks could be old and plastic does seem to break down over time. Just an idea and what I’ve learned on plastics while I worked for Black and Decker using various material to mold parts . It can be temperamental at times.

What fdp said. If you can't seat the nock all the way to the base of the nock's throat when you place it on the string, when you release the arrow the force of the string moving forward will force its way the rest of the way forward. Acting like a splitting wedge. You need a smaller diameter serving on the string. DANNY

I have been hoarding up yellow mercury nocks for years, but two months ago I threw all of them away. I would diligently work to make sure my string serving was a perfect fit. Two months ago the nocks started breaking and I had to different incidents were nocks broke on different bows. I like aluminum arrows and have now started installing unibushing in my aluminum arrows.

I have been hoarding up yellow mercury nocks for years, but two months ago I threw all of them away. I would diligently work to make sure my string serving was a perfect fit. Two months ago the nocks started breaking and I had to different incidents were nocks broke on different bows. I like aluminum arrows and have now started installing unibushing in my aluminum arrows.

I have been hoarding up yellow mercury nocks for years, but two months ago I threw all of them away. I would diligently work to make sure my string serving was a perfect fit. Two months ago the nocks started breaking and I had to different incidents were nocks broke on different bows. I like aluminum arrows and have now started installing unibushing in my aluminum arrows.

Could be too much finger torque.

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