If the only purpose of the screws is to hold the upper air frame on and all of the pressure will be against the nose cone ( the ejection charge is designed to blow the nose cone off), eight 4-40 screws should be more than enough. I just flew a mad Cow Pyron dual deployment kit for the first time last month. This is an all cardboard airframe kit. I mounted 4 “blind nuts” (brass inserts) 6-23 thread size in the forward bulkhead of the electronics bay and used 4 6-32 screws to attach it. Worked perfectly, and as far as I can tell there was no stress on the upper air frame. I like being able to take the upper air frame off to have easier access to the upper end of the electronics bay and the ejection charge holder. If you have more detailed questions cal me714-323-5968 Mike Michael Lesnick Axiom Healthcare Group 18135 Santa Lauretta Cir Fountain Valley, CA 92708 714-594-5720 - Office Phone 714-323-5968 - Cell 714-968-7076 - Fax MikeL@xxxxxxxxxxx From: roc-chat-bounce@xxxxxxxxxxxxx [mailto:roc-chat-bounce@xxxxxxxxxxxxx] On Behalf Of John Howard Sent: Saturday, May 28, 2011 8:48 AM To: roc-chat@xxxxxxxxxxxxx Subject: [roc-chat] E-bay machine screw ? Hi All, I've been a ROC member for a couple years and lurking on roc-chat for about the same. I am finishing a 4” fiberglass Madcow Nike Smoke for NSL/ ROCstock and have a hardware question. The Nike is one of two L2 rockets I am bringing with the hope of dong my L2 Cert flight. I have split the airframe in half and added an electronics bay built from a fiberglass coupler tube. I am hoping to connect it all together with machine screws. To load the ejection charge, I’ll unscrew the upper airframe, load them, then re-attach. The charge will eject the parachute out with the nosecone. Everything is built and ready to paint. I have drilled 8 pilot holes to mount the coupler tube to the bottom half, and four for the upper half. Do you think 4-40 machine screws will be strong enough, or should I use 6-32? Looking on the web, it looks like 4-40 screws would have enough strength, plus there will be 8 on the bottom screwed into standoffs/nuts. I could also epoxy the E-bay in, but I also have a open coupler tube with the same pilot holes so I could launch the rocket with a motor and motor ejection charge. The “keep it simple stupid” version. Thanks ahead of time, and see you in two weeks! John Howard Sent from my iThing