im building 16ft surf rod. what is the size of stripper guide should i use? 50 or 40? does it depends on the lip diameter of my reel?

I assume you mean "butt" guide (only fly rods use a "stripping" guide) and also that this is a spinning rod. Best place to start is with a guide that is roughly 1/2 the diameter of the reel spool. Normally this will work better if the guide is of a high frame variety. The only time I'd go larger is if I'm using very heavy, stiff line.

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im using 30lb 0.18mm braid with 60lb 0.47mm mono shock leader, fg knot.
which concept is better for my setup? NGC or new kr concept?

I doubt you'll find much difference between then in actual use. But braid is very supple and if you can get down to the choke guide more quickly without giving up anything, I'd do it.

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My first thought is that a chime-in on this topic from chris c nash would be great!

I agree with Tom that an NGC or K-R Concept would work well with #30 braid.

The K-R Concept actually has TWO specifications. Have you looked at the K-R + high profile belly specification?

Two K-R Concept Specifications:

Specification #1.) The "Normal" one has three Reduction Guides: 25H: 12H; and 6L or 7L. These guides are followed by a low-frame KB Belly Guide of 5.55mm or 6mm. KT Tip Group guides of 5.5mm or 6mm follow to the Tip Guide.
Specification #2.) The 3+1, as I call it, has three Reduction Guides: 25H: 12H; and 8M. These guides are followed by a high-frame 6L or 7L Belly Guide of 5.5mm or 6mm. KT Tip Group guides (as above) follow to the Tip Guide.

The difference between the Specifications:

Spec. #1 is the most Rapid Choke angle to the Belly Guide and through to the Tip Group guides.
Spec #2 lessens the choke angle to the Belly Guide and through to the Tip Group guides to help stiffer lines and leaders or knots make the transition. Very similar to the NGC, IMO. The difference between the NGC and K-R, however, is that you will likely save weight in your guide train with the K-R Concept. Higher frames with smaller rings keep line slap and friction at a minimum with less guide weight.

I'd invest in both Spec #1 and #2 guides for some tests. You'll only need to add an 8M guide to try both Specifications.

My take only. I'd like to hear what you find out works best for you!

If using a reel as small as like a 5000 size Shimano and single foot guides, you can get away with a 20h, 10h, 6l, to size 6 runners with 30lb braid even with a leader knot. You wouldn't even have to start with a 25, but...That shock leader makes me think you might be using heavier weights like 6oz with this rod and maybe you have a MUCH larger reel too and want double foot guides. What reel and what weights are you casting? The half the size butt guide always works with braid

yup im casting 6oz weight.
8000 size reel with a spool lip diameter of 60mm. what butt guide size do you suggest?

You can select a guide with enough height, a 25 would certainly suffice and a size 20 might get you by just as well.

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The height of the butt guide also plays a role in preventing line slap. A KR KL25H or RV25H is higher than size 25 V, SV, Y, KW, or MN style guides.
Norm

I personally think actual line slap is over exaggerated, it doesn't happen as often or as easily as it may have when lines were thicker, and stiffer many years ago. When things change, so should we, I have used spinning guides as small as a high frame 10 mm next to a 2000 spinning reel without line slap. I'm not the only one the first factory rods I saw built like that was in the mid-eighties.

Here is a link to a great discussion pertinent to this topic.

[www.rodbuilding.org]

Terrific information on the K-R Concept. The discussion gets into surf builds on page 2 and 3.

Spencer offers some good advice. Frame height really makes a difference and allows you use a smaller ring. One thing you really have to do is position that butt guide close enough to the reel so that the line can't traverse the inside circumference of the guide ring. You want to the line to lie on the bottom of the ring instead of passing through the center of the ring. This almost automatically removes any chance that you'll have line slap on the rod blank because as soon as the line hits that ring bottom it comes under control and begins traveling straight. Don't position it too close, of course, as other maladies will crop up in that case.

Test casting is the very best way to get a perfect guide system. It's just part of the custom rod building process.

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Simple test for most of us, just put your normal line setup and spinning reel on your casting rod and have a go, the worst case scenario, and build your knowledge from there, it will surprise you though how good it works.